Okay, just a couple more things:

When the game begins, will there be something stopping us from gaining power/abilities/gear?
If the group has a mek and a painboy, then it's entirely reasonable that cybork upgrades and powerklaws could be attached to various group members. Assuming we end up co-operating more than normal, we could feasibly elect a leader among ourselves. Would the leader then grow into a nob, as ork leaders tend to?

I asked about the terrain and kind of tasks we'll be facing because it will help players know going in what kinds of characters will actually be playable. Playing a kommando is perfectly reasonable, from a power-level perspective, but if we're never in a situation where one of us being sneaky would come up, then it's no different than playing an ork boy. Especially if we're expected to constantly be near each other.

These questions aren't me trying to manipulate things to my advantage, or to spoil the surprise. I've RPed in the 40k universe a number of time, here, on other websites, and even on the table top. The same problems tend to come up, and I'd like to avoid them where possible.
The 40k setting is massive, and deals with everything from grots to imperial titans in terms of scale. It's quite often a problem when people come to a game with different expectations of where on that scale they're going to be, in terms of both importance and potency.
It's also a setting capable of exploring every conceivable type of adventure. When people create characters who excel in certain scenarios, especially in an advanced thread where characters require a great deal of time and effort to create, they can be quite upset when they find out all that effort is for nothing.

When it comes down to it, I think this could be an amazing narrative with great opportunities for roleplaying unique scenarios, while also being quite fun. However, I also see all the potential issues, and experience has taught me to be weary of those things.