Higgs

The amount of force required to do some work will burn out a battery tool, especially the cheaper sorts. Mains tools can provide more torque.

If there is only a small area, I'd use a battery powered tool, for nothing too major. Anything more, I would use a mains tool.

I would use the seven-day period. But wouldn't start blacking until the third day. Two days to dry, from the jet wash, and scraping what needs scraping, up until the third day. Floating on the Monday (Monday to Monday), after three of four coats of blacking. During the hot seasons, it is easy enough to get two coats on in a day. Keep layers moderately thin, so the layers have time to dry. If blacking goes brown, after re-floating a boat, the boat went in too soon. The other obvious sign would be an oil slick at the waterline.