Well going through it in order;
Warbosses - you really want a klaw on them, since they're going in a unit with a nob/nobs what I'd do is stick the klaw on them and give the nob a big choppa. That way the nob can take challenges and its no biggie if he dies. Then you've got +1A with a S10 klaw on the boss. If you have any spare points, the first thing you should look at is an attack squig.
Shoota unit - stick with big shootas rather than rokkits. Cheaper and the rokkits generally have a different target profile plus they're not that great against vehicles. Would also upgrade the nob - big choppa if points are sparse so you at least have some high strength hits in melee.
Sluggas - yeah cool
Nobs - Thats quite a few, and they're quite pricey to boot. 4+ save is okay but also is easy to deny. I'd loose all the 'eavy armour and grab a painboy instead. Then get cybork bodies on everyone so you've got rerollable 5+.
Stormboys... an annoying unit through them not being as good as I feel they should be, but still use them regardless - unless you going to take zagstruk not much else to change but he costs a bit for something thats kinda nice when it sporadically works.
Warbuggies - kinda made of paper, just leave them with the big shootas to keep them cheap. Leave anti tank to klaws or guys who can hit stuff (grots or lootas) at range. They're not terrible against infantry but will probably be seeing more action as a screen for the trukks.
Warbikers - definitely want some high strength in there, a klaw or failing that a big choppa. These guys can work at tank hunting with a fast
pk.
Lootas - yeah like you said
Deff Dred - probably not best to kit him fully with
DCCW. Often wouldn't need all those attacks and also becomes so avoidable for the enemy. I would suggest either 2 big shootas or skorchas or c-c-c-combo
Killa kans - also made of paper but at least a stronger grade. If you want grot fired rokkits... stick to big guns, they'll generally last longer and have greater range (yes they're static too...). If you are going tank hunting with kans, take a kustom mega blasta, at least you get the ap2 benefit for penetration. Or grab grootzookas to keep them cheap and screen the dred.
Thats pretty much it the main things though:
- nobs unit, get a painboy
- warbikers, get a powerklaw
With what else you have, I wouldn't really suggest changing any units; just the composition of the current ones. And dont rush up the centre table, the trukks will die and everyones stranded. Just go up one edge and make it yours - kinda what everyone does though so