Where do I begin?

[Bushwacker]

You could call your local county Waste Management outfit about the old gas. I think the household hazardous waste disposal place would take it.

I've seen old lines full of crud when they sat a long time with fuel in them, so you might want to replace the primer bulb and all the fuel lines from the tank to the motor. Might also check the lines on motor from fuel pump to carbs for crud also. When you get the tanks clean and some fresh gas in it, if motor won't idle right, the carbs may also be full of crud, so you may have to disassemble, clean and rebuild them.

Do a compression check on motor to check for stuck rings. If one or two cylinders are low, might try runing some ring free or equivalent decarb stuff thru it. (Do this with the OLD plugs in it!) I'd also change water pump impeller, which may be full of cracks from sitting a long time.

That transom crack may be just some filler that didn't bond well, but I'd open it up and make sure it's not thru the laminate into the core before launching the boat. Those stains and bubbles around it look a little suspicious. If just cosmetic, might be able to repair with epoxy filler. I would not use polyester filler below the waterline.

The gel coat cracks up on the gunnel & top of transom look like maybe some extra gel coat was laid on pretty thick. That stuff is very brittle, so once it gets over about 0.032" thick it doesn't take much stress to put a lot of cracks in it. Will probably have to sand/grind it off, repair with epoxy and repaint.

It takes a lot of work to bring a boat back to life that's been sitting a long time, so good luck! This forum can give you a lot of good advice on stuff to check. I'm sure there's a lot I missed!