Pro-tip for last wave: You only need to damage mega-copters by around ~30 million damage for them to drop the bosses (snowmen, demons, spider-queens) so grab your long range DPS character and drop those annoying spider-queens off the map before they even reach the tiles, leaving you only having to deal with the mega-copter. This significantly speeds up the last wave. Most mega-copters seem to spawn to the lower left and upper right corners of the map.
1st wave I build everything except warden towers and build them during combat wave, also have upgrader adept out.
My 4 character combo: Summoner with 2x huntress guardian, warden, hb monk, tb monk.
Kudos to Zwanzigernuggets and achennito for their great builds, used them as an inspiration.