Both of you guys, the first thing you should absolutely do is go at the
deck and get the
gelcoat to shine, then wax it. It's not just cosmetic; it protects everything underneath and once
gelcoat start to deteriorate, the longer it goes the harder it is to bring back, and eventually it will fair altogether, requiring more time consuming and expensive
repair.
To clean the deck and topsides (hull between the waterline and the deck). I would use Mary Kate ON/OFF, available at most
marine supplies. It's basically an acid, but it will take almost ANY stain off. Keep it off your skin, and
paint and
aluminum if possible, or rinse those areas immediately. It's a great prep wash before compounding and waxing.
As far as the
interior goes, I would pull the cushions out and wash the covers as best you can. Dry out the foam and if it's too far gone you might want to replace it although good foam is surprisingly expensive.
Go at the mold/mildew and get it out, wiping down surfaces with white vinegar as a last step; the acid in the vinegar inhibits
mold growth, to a degree.
If there is a lot of
mold it means moisture is potentially getting in the boat. Check every through-deck fitting; if they are hidden under headliners or in cupboards, open them up and check. If a fitting on the deck is leaking you need to fix it, not only to simply keep the water out but also to protect the
core of the deck. It's almost certain that on an '85 Hunter something on the deck is leaking if the previous owners have done nothing.
Also, get a dehumidifier for the boat and leave it running when you're not there.
There's lots more to do, obviously, but those are two things I would do right off the bat.
Oh, of you can get ethanol-free gas for your
outboard, do it, particularly if you don't run it that often. If you can't get ethanol free gas, put a
fuel stabilizer in the gas mix. It won't cure the problem but it will help.