Scott,
Welcome aboard! Now, on to stress cracks. The proper way to fix them is to dremel each and every one of them to form a v-groove, then fill with glass (2415 and resin), grind flush, and gel. You also might want to see if you can tighten the rail bases, as the flexing at those points is what is causing the spider-webbing.
As far as motors? 250 Etec. She'll easily handle the 300, but the 250 will save you some bucks. You'll love it and you don't have to change your rigging. Don't worry about it being over-powered. The weight of twins would be the real concern, and today's twin Etecs are as light as their old brethren. BTW, we build Donzi (our sister company) 23 ZFs with twin 225 Verados for Missouri law enforcement. Not much lamination difference. I wouldn't worry about a single 250 Etec...
