New to the game : questions in currency, guns, mode

Hello ! I’m rather new to the game and I’m still figuring it out, as they are so (some would argue too) many ways to play and acquire things.

Question 1 : how can I spend my currency with clothes on it ? Could not find where

Question 2 : where can I use my BP currency ?

Question 3 : what gear would you advise for metro mode ? I am starting with a simple uzi, good bullets, sniper, helmet level 4 rest level 3, few bombs, MO and med kits

Question 4 : on the normal mode, what guns that can be found rather easily would you advise ? I usually take some kind of uzi or 9mm with a 5.6mm, usually an M14 or smth line that

Question 5 : how would you advise to train ? How do I find good teammates ?