You can deploy whatever you want, including units that you are using or that have a bonus. Whether that is worth it or not (generally it won't be, obviously) is up to you.
I'll comment on these last two, and then we need to take the discussion of WD matching issues to another thread. The matching in Full Assault will very likely be more complex due to there being three factions fighting at once.
No, I'm saying that we don't control who is available to fight at any given time.
The top 10 teams have to fight somebody. If they've been in the queue for long enough that the search parameters have widened that far, top 50 is possible. We've already made some changes to lessen the chances of repeatedly getting the same team and we've balanced things about as much as we are currently able to. I know that is not happy news in this case, but it is the truth.