i'll only answer #3, and the only answer is simple...simple maps make the game fun, take ideas from ijji & nagi [HellSniper] they're the best map makers for gunz imo. they keep the maps simplistic and balanced.
also, it should mirrored / where the team starts and paths are equal and balanced. (Mansion / High Haven)
one cant have to many "choke points to hold" or important places.
For Props, dont make to many please. makes the map alot more laggy, and the detail might be to much to remove the so called class away from the map.
but think simple.
just an example, really dont do it o.o..
two large towers/buildings, whatever.
2/3 layers of bridges, one at the top, one at the bottom and opt: one in the middle connecting to a tower in the middle (like a king of the hill style.)
that way you have two teams attacking the middle tower, and maybe even attacking the enemys tower. horrible example sorry D:< im not a map maker lolol
