Blasting to white and immediately sealing with epoxy is the way to go, and should do fine. This time of year it'll be a challenge unless you're indoors.
Once sealed, you can use any filling/fairing compound that's epoxy compatible, but look for something easier to sand and fair. How badly pitted is the keel? How much filler thickness are you likely to need?
Great little starter boat, btw, it was our first too... (30 years ago next month!!)
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)