Personally - first year, scrap off any loose stuff and put a coat on. Launch and enjoy.
Gnerally speaking its pretty frowned on to rub down anti-fouling. Toxic, nasty, gets in your lungs, hair, mouth etc. Neighbours in the boatyard get miffed if they are downwind and the Green lobby are pretty unhappy at the toxic stuff ending up on the ground. That said, it didn't stop the nettles unneath me this winter! A complete removal does tend to depend on how much build up you have. Self eroding types of anti-fouling do just that, reducing build up but certain parts of the hull are more sceptible to 'wear' from water flow, hence eventually it starts getting a little uneven. I can anti-foul my 32ft of wood in two hours - or even less - using a roller. Taping up the waterline takes a good 15 minutes of that. I have only ever did one complete strip of the bottom and that's so long ago that I can't remember how long it took. Did a partial burn off this spring which was taking me best part of a day to do one side! But then I have a lot more under the waterline than you.
Unless it's desperately flakey I wouldn't be over bothered.
Again, agree with the above. If you find any spots from which the antifouling has completely gone it would be a good idea to touch these in with a compatible primer before applying a bit more antifouling.
With regard to winter preparation, it is not necessary to remove all of the old stuff every year. A bit of WET sanding before repainting is a good idea; use some very coarse wet-or-dry paper and keep it wet to avoid dust. My nephew did mine last year and it took him about an hour (well, that's what he is around for )
Two years ago, I took mine right back to wood. With three of us scraping and applying paint stripper it took about four days of not particularly arduous work. Paint stripper is excellent, but make sure it is compatible with your hull if you have GRP. I'm lucky in that I have a wooden hull (you won't hear that sentence used too many times!) so Nitromors worked well.
I don't remove old a/f - just a rub down (make sure it's wet though) and then on with the new. Two even coats seem to be effective for two years on my boat. Something for next winter tho. Just go sailing whenever you can.