even when ya soda, you hit it with the sander after... i'd strip it with the DA, epoxy.. with 80, you'll be going thru in most spots anyway... better to have one, even substrate, as opposed to tons of featheredged paint/primer areas that could possibly cringe with primer...
the sander is fine, the 20 gal of the comp will be your limiting factor... might have to stop every few minutes to let it catch up...