[slipacre]

Fuel tanks can be either easy? or hard depending entirely on how much you have to rip out to get to them.
Engine - have learned that cost of rebuild is mostly labor and that usually a lot of that is removing the engine from the boat to do the work because there is not space to do it onboard. (then replacing the engine)
Bottom job - you did not mention age of boat and how you want to deal with blisters if there are any. Just a paint job is one thing stripping and doing an epoxy barrier coat is another few thousand.
I had two boats fail survey because of moisture issues in deck and or hull. Three years in the water - you should have the surveyor look very carefully at this.
Good Luck Todd V