Response to 2nd list;
For your
HQ you want to think about what they bring to the table. The lord commissar holds units in place, you've only got 1 blob and 2 vets to benefit from this who probably wont be within effective range anyway. A better option would be a
CCS with a regimental standard and then maybe add a normal commissar to the blob itself. The primaris with pyro?
mmm ok but then I dont use psykers much.
Your infantry squads cant take both a flamer and a meltagun, only one or the other. They can get a special and a heavy weapon though. It's not best to mix heavy/special weapons in a squad. Missile launchers aren't fantastic, infantry; frag<autocannon and tanks; krak><lascannon. But in this case I'd scrap the heavy weapons team and instead divide them up in between the infantry groups.
HWT are a bit fragile by themselves. In the squads I'd either take flamer and autocannon, or meltagun and lascannon depending on their role.
Vets have the same issue, a meltaguns popping a tank, a plasma wont help much against AV13+. And vis versa, a meltagun can knock out a terminator at 12", but not 2 terminators like a plasmagun. So take one vets squad sole meltagunners and another plasmagunners.
LRBT, sponsons are template so they cant snapfire. You dont want snapfiring sponsons regardless so take the
LRBT raw, even the hull lascannon could go.
Scout sentinels, the only sentinels with potential. I'd loose the hunter killers, your paying 30pts for 1.5 hits which is almost another sentinel. Once again I wouldnt go with missile launchers. Only options I take are either autocannons or the multilaser and outflank. The bs3 kinda deters me for 1 shot weapons when they'll probably all die the next turn. Keeps them cheap and reasonably effective.
I agree with somedude about the allies not bringing much benefit. It looks like a lone captain who will be jumping around by himself and some stationary marines putting in some fire.
IG doesn't need help with putting in some firepower. For the 340pts for your 2 blood angels tactical squads you could get a LRexecutioner with plasma cannon sponsons and 2 chimeras for each veteran squad to go in. I believe that would bring alot more to the table so your current
LRBT doesn't immediately get pummeled to dust and rather than 2 plasmacannons that overheat, you've got 5 that dont. Then if you lost the captain, could get another meltagun vets squad to go with the vendetta with points to spare.>
"I'm making a Tau army in Warhammer 40k, is this a good idea?" No tau army's a good idea 
