Fiberglass and epoxy would be your best bet, but you'd have to do both the inside and outside of the hull to completely seal the wood and prevent movement. As long as the epoxy and fiberglass are never penetrated, allowing water in, the boat will literally last forever. As you've already started to build-in the interior furniture and can no longer reach all parts of the inner hull, this really isn't an option anymore (unless you want to disassemble everything).

The next best option is to seal and paint the hull as you would normally, and then use hot tar, tar paper, and thin sheets of copper nailed to the exterior of the hull with silicon bronze nails. The copper sheeting will prevent any kind of growth on the hull, lasts pretty much forever, and will prevent Teredo worms from ever paying you a visit. It also has the added benefit of never having to do bottom paint/anti-fouling ever again. I would definitely recommend this option for your boat. If done properly, it'll pretty much last forever.

If you've already got a leaky deck, you need to handle that ASAP. I cannot stress this enough. The thin layer of paint you put on the wood is not going to protect it. When fresh water hits that interior wood in the bilge, it will begin to swell and rot spores will come to life and quickly turn your boat into the same chocolate cake consistency you had when you bought it. Keeping whatever you've got stored below decks from getting wet is a secondary concern. You have to keep that fresh water out. Seal that deck!! No matter what it takes. There's no such thing as just a little leak or drip here and there. It's insidious and you won't realize the damage until it's too late.

Lastly, paint everything that the sun is going to touch. I know, I know, the wood looks so pretty, right? I'm a woodworker, I love looking at the stuff, so I get it. But UV radiation will deteriorate the wood, regardless of species. It will weaken, and crack, and then eventually just fall apart. Yes, some people varnish exterior wood trim, sometimes adding a UV blocker to the mix, sometimes not. This helps, but it'll become a never-ending task and it's not foolproof. Paint is. The pigment solids in paint will completely seal and protect the wood from UV radiation. There's plenty of pretty wood to be varnished below decks. Paint everything outside.

Just my two cents. Glad to see the build coming together so nicely. You'll be out on the water before you know it.