Questions re first seacraft project: a '73 Tsunami

[sate888]

Hey everyone, I've been wanting to log on for weeks since I got a 1973 23' Tsunami on ebay that seemed to be not too big a project risk for my skills....but until now I would just be exclaiming at how well the boat is built, so I forced myself to wait until I had been through the boat enough to have some real newbie questions.
First, I filled the thru hulls for the old marine head and pulled it...is that ok?.....I didn't just ruin a classic did I? I plan on a portapotty to avoid having a holding tank.
Next, is there much danger on these boats of the foam that seems to run on both outboard sides soaking up water? (I've had several Whalers.) I think I can see through the engine rigging boot holes that there is foam showing under the two livewells on the counter, is that ok? Should I core it and if it's dry seal the raw foam by pouring epoxy over it or something?
Another, unrelated, question: I have heard that in the original open transom/splashwell configuration that I have these boats can sink if the pumps or battery die, and it does certainly seem that the rigging boots are very low. I planned on glassing in the port hole and running the battery and fuel lines thru a new stbd rigging boot that I seal as well as possible with tape, with the idea of eventually raising that stbd boot hole at least a foot. I would do it now but I'm dying to get her into the water and I don't want to dissassemble all the rigging to re-reeve it.
Also, adjoining that stbd side rigging hole is a roughly 5"x3" hole covered with wood....what was that for? Can I safely close it up? Don't like holes in my boat......!
Finally, for now anyway, my fuel tank appears to be in good shape although it's got some sort of fiberglass sheet over it so I'm guessing it might be original? I pulled about 30 gallons of old fuel out of it, but before that there was no gas smell or oily bilge after 60 miles of trailering her home, so it might actually still be solid. But the 4 wood attachment pieces are rotted. I will replace them with teak, but, and here's the question, are there other tank hold downs I should check?
Attached is one of the original pics from the ebay listing, I have more if anyone's interested.....she looked kinda rough, it was only a 3 day auction and no inspection was permitted so not many people seemed to be bidding.
I hope to eventually awlgrip the boat, fill in the transom, and put a bracket and a 300hp 4 stroke (leaning towards Suzuki new but trying to find a used Verado as well, the Yamaha 6cyl is too expensive new and the 8cyl weighs 800# which seems like it might mess up the trim and self bailers), and I have been looking at those threads on this site for the best transom repair technique (from inside or outside) and bracket vendors for this model, so any thoughts would be greatly appreciated. Even better would be a bracket and a 300hp 4 stroke anyone wants to sell.......
But I plan on running her with the 1986 Evinrude 225 she came with to get to know her first....I've owned a number of boats, but never a Seacraft, so I want to make sure she suits what I want to do, which is general fishing and diving stuff but also fuel efficient Bahamas trips in settled weather (planning on a high thrust 9.9 as a kicker for safety in crossings). I know 23' is a bit small, but these hulls did the Miami/Bahamas races and I'll have a liferaft, gpirb and satphone.
Thanks for your thoughts....!