I'll go ahead and warn you that Bravo 3's were notorious for escessive corrosion. Too many dis similar metel parts cause it to corrode faster. I think they may have changed some things after the early models so you may be OK.
Every year I usually have the drives pulled to inspect U-joints and bellows, so far we have only had to change the oil annually. We don't have a trailer and keep it on the lift so we usually have it all checked out anytime its hauled out. 500hrs so far so good on a 24ft sea ray. On a high performance application I'd recommend servicing the outdrive every 25-50 hours depending on abuse. Might want to look at Merc's recommended service.