Speak to the manufacturer before you buy one - they can tell you whether any of their RIBs have been coded and meet the requirements of the MCA - and whether any of the stability stuff has already been done. If they supply coded boats direct from the factory themselves, they might have a list of kit/equipment that you would need to fit/buy to reach the coding requirements for the category you are interested in.
RIBCraft were very helpful when I was coding mine (it wasn't coded when I got it, although I always intended to at some point) - I don't know whether other manufacturers would be more or less helpful - but can't see a reason why they wouldn't be.
