You only actually need five for boosting almost all of the achievements and that is only for the 4 kill ultimate achievements. You need 7 for the anger management and 5 for rapid discord if you don't do the reaper method. Most of the rest of them can actually be achieved with just two players. One on each team. I don't mind to help you and I have several boosters on my list at all times of the day. Personal message me and I can set you up. I'm not going to post my GT though.
I'd be willing to help with any if someone can help me get:
The iris embraces you
If anyone needs any achievements, and can help me with any of these, please message me on Xbox, GT - finelete