Dont worry about the trigger, it has a plastic housing but the trigger sears are steel. I have been running 600 fps for about 2k rounds through my MB05 and the trigger is still tip top. It depends on what you want to do with it and your desired velocity. For accuracy get a tight bore, use heavy weight bb's, get barrel spacers, and a new hop up. the MB05 are fully type 96 compatable (not marui 96, or tanaka) so any after market parts that say type 96 will work. For fps upgrade then you will need to rebuilt the whole top end as well. I would recommend you start with the barrel and hop to increase accuracy.
and use at least .3 gram bb's if not heavier.
and use at least .3 gram bb's if not heavier.