Welcome to the forums, Nick.
As to rebuilding rotary is not that far off from rebuilding piston engine, i.e., piston engine's NORMAL rebuild cycle is around 100K, and some even longer. Same as for rotary engines, it's NORMAL cycle of rebuild is about 80K but, there are rotaries with nearly 200K on it and still runs.
As to reliability is concerned it's based upon how well you maintain your engine just like piston engines. It will treat you the way you treat it
Apex seal, 2mm and 3mm...3mm would, obviously, seals tighter and it gives more of snug fit sort of speak and thus, gives chambers with better sealing, in turn, gives more whomp from cycle. However, in a event of seal breakage 3mm has greater chance of damaging housing.
Hope that helps a little.