[Trigger] Help with some problems

[mateuspv]

Hello, I'm making a map where the objective is to survive as a team, but I'm having some problems like:
Do not know-make a system where each player has 30 seconds to buy skill, and then be moved to the center of the map where the enemies appeared and when the enigmas are killed all over again.
Enigmas-units do not attack (and I think a simple problem to solve but do not know)

Well, see how the map is simple but of great importance to me, I'd like some tips on how to solve these two problems above, I appreciate any help.

sorry for the English ... google translator
if I posted in the wrong area please tell me where to post

thanks for attention