When you say i could take those do you mean the wraithguard or D weapons? didn't think deathwatch had any if so.
You can probably take the Eldar. Low enemy model count is good for you
So i can't use kill teams at all in this only mission tactics? Seems kinda redundant when the name of the formation is literally kill team lol.
Kill Team has its own specific Detachment you have to use. 0-2 Troops, 0-1 Elites, 0-1 Fast Attack. No Formations for you. Or for anyone else, so there's that.
As for anti tank i actually looked around and though of going with a vanguard vet with a power fist over the biker, can jump and move alot faster than everyone else and can pound through the armor with relative ease. I didn't think too much about armor as i didn't think many people would be able to field them but yeah it's stupid to rule that out.
Power fist would probably work better than the Frag Cannon in the anti-vehicle role, as the vehicles in Kill Team will usually have 10 rear armour (with a very, very rare 11/12, usually on Walkers). The important bit is, you NEED anti-tank
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.