As I previously spent an entire summer grinding away decades of bottom paint, with
24 grit to get all off, of course I violated the gel coat badly and had to fair out entire keel
with West System fairing compound, long board 80 grit sanding, then four coats of barrier
coat 2000 from Interlux. In retrospect I would soda blast the entire bottom, done in 1/2
day, can paint three coats of barrier coat in the afternoon, and balance following day.
At that point you are able to apply your bottom paint and commission boat in several days. If you do not want to go deeper due to the condition of your keel, I recommend
80 grit sanding, several coats of barrier coat then apply your bottom paint of choice.
This will add many enjoyable days of sailing not sanding. Based on the type of paint you
elect predicates how fast your keel will be. You cannot burnish ablative paint however
there are numerous hard bottom paints that may be burnished and will be faster.