Cadian forces are happy only when static. Each tank, troop, whatever, rerolls its 1 when sitting on its butt, but loses to hit accuracy on its heavy weapons when moving at all. Cadian heavy bolters suck on tanks, for example, because leman russ (4bs) on the move (5bs) isn't going to often hit its target. Spending 2 command points every roudn to offset this against ONE specific target (interlocked fields) gets expensive in command points very fast, but is an option.
Tallarns don't take ANY such move penalty -- and have a few tricks built into their tanks that let them move 5.9 inches, prepare to fire, and then move a bonus six inches before OR after shooting at full efficiency. Several leman russ commander tallarns will give your army a surprising ability to use even its shorter ranged guns like the punisher -- while dodging slower melee threats that try to trap you. The small point difference between a tank commander, tallarn, and a tank, cadian, in cost is more than offset by changing it from a 4+bs vehicle that can move only 5 inches, to a 3+ vehicle that can move 11 inches, while still double shooting. An enemy that catches a tallarn tank will still neutralize and kill it, but at least they have the mobility to make chasing them a somewhat frustrating experience for many armies. Running this whole shooting match as tallarn is a pretty good idea, and reading up on the specialist detachments (d4chan has a good summary) of the emperor's fist and blade are also on your homework list, if you haven't used them yet. Surprisingly punisher gatttling cannon works really well on the tallarn tank commander -- so perhaps drop 1 of them, make the other three commanders, and put the rest fo the points into infantry below. They can pass orders to themselves to keep moving near the front, and the slower, but longer ranged lascannon tanks do NOT need multimeltas (which force them to come close to the enemy or are useless). Save those points for a couple of astropaths and an engenseer, which can protect the lascannon tank battery with spells and repair it. Set that up at the back!)
If you are fixed on cadian, just substitute the word "cadian" for "tallarn" in all comments below, but it will feel clunky to you in performance with the tank commanders.
Oh, and you want a lascannon on EVERY leman russ, in this list, because that means an enemy can't shut off your antitank easily at all, the lascannons have both decent range and decent punch. You will often nearly kill a big target with your main antitank effort, and pick up the spare with various potshots later (missles, lascannons from various corners of the board, etc,)

Your plasma sentinals are poor in melee (experience tells me its a waste to even buy the chainsword, it won't get them out of a fight, and they can't shoot if they are in it.) They are going to have to move to get away from melee, because even a 36 inch weapon will let many armies be on them in 2 rounds. So they will suffer a -1 to hit with a weapon that on a 1 CAUSES THEM TO DIE from their own shooting. Add to that the fact that they aren't going to hit much, statistically, they should all kill themselves by turn 3. (One good turn shooting, then 2 turns run and gun, with 2 shots average per sentinal, means by turn 3 they have all died from their own firing.)
The other "range" heavy weapon options for sentinals are both 48 inches, which means they can set up in a spot where the enemy may give them TWO turns undistrubed shooting, and then run arodn the board shooting with no chance of self destructing, even if they miss a lot. Lascannon are good anti-armor, and some opponents may feel your tanks such a higher priority that they don't bother to kill that one shot sentinal over there. Missle launchers do both, and a missle launching sentinal is a fairly low priority target in a 2000 point list ... but six of them start to matter. I ain't saying don't take them, but take them in a manner you have a plan to use them that won't just cause them to be neutralized at your expense.
A strategem exists to give 3 sentinals a +2 to hit on the first turn now, from the book that was leaked today, which makes 3 lascan sentinals in one unit a very atractive turn 1 idea. Make the other 3 rocket launchers for variety, maybe, and you have a good little moving wing, whcih the enemy may not bother to shoot at until AFTER your three lascannon big tanks die.

. Tallarn troops can incidentally move normally with missle launchers in each squad and fire them while moving without penalty, giving them a long range punch nobody expects from gaurd soldiers. They can also carry grenade launchers for the special, and a bolter for the sarge. That (54 point) is my recommended loadout, it has anti-horde and anti-armor and it doesn't break the bank. While not EXACTLY as fast as your tanks, the running infantry can use their commander's orders to movemovemove to stay in pace with the pack, when not actively shooting. Lose the tauroxes to gaine 144 or so more points, and use those points to buy 3 more infantry. that leaves you 24 to pass out a few grenade and missle launchers, giving you an elegantly fast flowing infantry that can do its firing while keeping the distance from the foe. Yes, you will win by running away, or not at all! The missle launchers can be configured as antitank OR antihorde, as can the grenade launchers, meaning your 60 troops have a lot more versatility on the move than your 30 troops did inside tauroxes. "Movemovemove" makes them roughly as fast as tauroxes, anyway, so you can whip them across the board like nobody's business. In the late game, platoon commanders can use that order on themselves to suddenly leap from cover, zoom into position, and nab objectives when the enemy doesn't expect it. So you probably want a platoon commander trio to jog along with the troops, rather than voxcastes and a special weapons team to send an order across the map.

Your army has some real weak points to it still, but its got more troops to screen, a more mobile armor element, a more cohesive long range lascannon element, sentinals that won't explode, and some repair capabilities and denial capabilities, while still retaining that "I am a mobile as heck armor company" feel. It won't win tournaments against marines, but I would hazard to say a poor player with marines migth find himself in real trouble against the firepower and mobility combo. Oh, and convert pask into some sort of other leman russ, to put in to the spearhead with the rest. Your enemy now has to prioritize targets in an unfavorable manner -- you have several valid possible target groups to worry about. 3 lascannon tanks picking off heavy armor across the board, 3 sentinal lascannons getting that alpha strike, 3 tank commanders (I personally run the tallarn tank commander only ever with a battlecannon and lascannon and 2 plasma cannon or demolisher cannon, a lascannon, and 2 plasma cannon. The long range ones often have an easier time but the shorter ranged demolisher cannon is a murderball on wheels.) .. that starts to become more armor than even the firepower of modern lists can quickly degrade.
Putting all that advice together (and bearing in mind its not the most compteitive army and I just plain ignored the PA book that came out today that would alter this some) .. a traditional (last week) tallarn army using your elements might look like...

mobile infantry 2 battalions 454 points (tallarn) (The Herd. Start as screens / run after tanks)
2 company commander with a bolter each
3 infantry squads each with missle launcher, grenade launcher, bolter
1 company commander with a bolter
1 lord commisar with powerfist and boltpistol (he gives a nice buff to leadership for the troops, and he is a beast in melee by gaurd standards. As your slowest officer he will quickly end up at the back wher ethe melee is likely to start.)
3 infantry squads each with missle launcher, grenade launcher, bolter

Mech side 1546


tank commanders, mobile sentinal wing, (Point towards enemy.)
3 tallarn tank commander
1 punisher cannon, 2 plasma cannon, 1 lascannon, 1 pintle mounted stormbolter each (they can murder troops now, but still threaten armor some) (I thinkn they are 192 each but doublecheck me!)
3 sentinals (squaded unit) with lascannon
1 sentinal (loner) with missle launcher

Lascannon battery (start near rear, all these guns prioritize big things at range)
3 leman rus anihilator with lascannons in the hulls but NO meltamultis (as they are shorter range and expensive!)
1 leman rus generic tank with battlecannon, lascannon
Repair and support wing 45 (start near battery to enhance its survival)
1 astropaths (one grants +1 to armor save, and one grants -1 to be hit, I think either would be great for your armor)
1 engenseer (probably start him beside the lascannon tanks)

Blend these into 2 battalions, 13 cp, and all the leman russes can be emperor'rs fist (for 1 cp) and get objective secured.

That's 2000 points? Its not perfect but I think the parts of this list will mesh better than the parts of the list before, basically removing things that have ranges or abilities that don't mesh with what I think you intended as their battlefield roles. Antitank, you now have the lascannon on all your leman rus, as well as the lascannon battery and battlecannon turrets, and the plasma guns on the tank commander, and the sentinals 3 lascan+ 1 missle (safely!) and the 6 rockets and 6 grenades from the troops. Its decent pressure against tanks. Antihorde, you have all the lasguns + 6d6 missle frag + 6d6 grenade frag + 1 d6 from the sentinal + 138 shots from the tank commanders. I think you have good threat pressure against both now, beacuse the weapons are subtly longer ranged and you can really use more of your army to shoot at a given threat in any round (than when you had to get multimeltas or such close enough to do so.)