1. macs tuned pipe, yes you will most likely have to tune in the engine again any way.

2.I'm guesin the boat is used then? if you want performance get the new shaft off www.offshoreelectrics.com and some new carbon prop props to try.

3.If it's the stock ya 30% is prolly as high as you want to go,any higher and your probobly asking for trouble.

hope this helps