1. As already stated, the Geo2 takes Ego10 triggers.
2. A better paint to barrel fit (if not good already) will certainly help matters - shooting small paint through a large bore will waste air.
Check if you have excessive blow back up the feed neck. If you do, try changing the bolt tip o-ring.
If the vent hole behind the can o-rings is larger than a pin hole (it should be 0.3mm wide) then that would waste some air.
The back check ball in the solenoid should be clean, undamaged (no nicks or dents) and round in shape. It should also be between 4.00 and 4.10mm optimally - a little larger is fine, but smaller isn't good.
You could try dwell tuning to improve efficiency. After setting your velocity with the stock dwell setting, find the lowest dwell setting that maintains that velocity, without shoot down in rapid fire.
Check the marker, reg, hose, fittings and tank for any leaks, and eliminate them.
Fill the tank slowly to prevent heat build up, and if possible, top the tank up after it cools. If your tank is filled quickly, and gets very hot, you will loose pressure as it cools.
Chances are that if your marker is very new (use wise, if not necessarily with regards to purchase date) then it could well improve with use.
3. Yes. 12.5ms is the stock dwell setting.