BatfinkV is far, far better than I am, but I'll give what I can.
1) 50% fuel or 25% + DTs unless you know you are going a long, long ways. 100% fuel on the Mosquito is about 3,500lbs of fuel.
2) Rockets are very draggy and they leave very draggy rails behind, don't take them unless you really want them and don't mind shaving 10-15mph off your top speed.
The Mosquito is about speed and anything you clutter up the airframe with costs you speed. The shackles for the external 500lb bombs cost you 4mph after the bombs are gone. I don't know about the DT shackles(I always take 50% fuel), but I think they may be the same.
The Mosquito's WEP is very potent, use it, but be aggressive while you have it. Short snapshots from the Mossie will end fights. She does not turn terribly well, but she does handle the vertical pretty well. Use yo-yos to cut inside of better turning aircraft.
I'll post more if I have time or if you have specific situations you'd like to discuss.