Obviously lots of this is up to personal preference. Lots of opinions.
To clean the stains on the hull, I use Spray Nine boat bottom cleaner. I tested many and this one works the best. Wet, spray, lightly scrub in with a soft bristle brush, let it work a few min and pressure washer off.
To remove scratches, same as a car. In fact, gelcoat is even tougher (but it CAN still burn if you put too much pressure/friction). Normal buffer with the usual compound. The grit level has to be adjusted to the depth of the scratches. You can even wet sand it and work your way too a finer compound to a fine polish. I've worked out major scraches out before. Once she's all scratch free (and that part takes a lof of work, don't underestimate that), then you can finish her off with either a wax or ceramic spray coating if you want it to last longer.
I use 303 on my plastics/vinyl fairly often to help protect the seats from sunscreen stains and sun damage.
I use my leaf blower to get the bulk of the water off and then wipe down the rest with a microber towel/shammy.
All of that being said, I treat my boat as a boat. Not as a showpiece. I don't go crazy. I don't overdo it. My boat has plenty of little scratches, dirt, etc. I periodically clean her up. Once a year I usually do a more thorough job, usually in the spring after I come out of hibernation. And I accept that it's a boat that will get dirty and worn over time.
