Laurie,
Welcome to the powerboat club. Please raise the limit on your credit cards.
As others have said, maintenance is key, but especially so I have found on engines & drives running on the edge. And parts are $$. One other word of advice for when the go faster bug hits: HUGE differences in marine engines and auto BB Chevies. Get adivice and /or your rebuilds from marine folks. For example, a standard street BBC cam will cause water reversion on boats (due to the mixing of water and exhaust) - water reversion causes engines to grenade. There are ways to deal with this, but the cams are usually different. Auto engines run at 100% load maybe a few seconds at a time. Powerboats boats are at 80-100% load for hours.
Since you're going to cruise salt, make sure it has a closed cooling system OR no aluminum heads and only marine aluminum manifolds. Either way, flush, flush, flush - at least 30 minutes per side.
Here are some sites I have found useful:
Forums:
I usually only cruise Offshore Only. It deals with the engines & drives you'll have as well as the quirks of offshore boats. Probably more general experience there than the Baja forums; like here I found they are very willing to help. I've had marine mechanics PM & call me to help me DIY.
http://www.offshoreonly.com
Of course, the Baja forum as pointed out will be good for Baja specific questions
Parts places I've used and had good experiences:
http://www.marineengine.com/ Cheapest I've found, and has accessories also. Sells OEM & aftermarket parts. For OEM, I'd check around though
http://www.perfprotech.com/store/default.aspx
http://www.dougrussell.com/partscatalog/index.cfm
http://greatlakesskipper.com/ Good surplus dealer, great deals on new take offs, etc.
Let me know if you have any questions.
Andre