Old vinyl will come off easily with a windo scraper. $1 at any hardware.
Gel coat will be lighter there so easy to re stripe.
Two pots easy to use if you follow instructions and you can wet and dry for any dribbles.
To find leaks put water in hulls and check usual places. keels and board casings.
Invert hulls and repeat. This is when you will find the leaks. If the boat has been outside for any time a bnucket is not that much.
Make sure you can reach front beam and front of board casing and the chain plates from the inspection port. I have never worried about putting insection ports wherever I wanted them and have run into no trouble.