Hard to judge your home space question, as far as mites & quarantine, but unwanted transfer of parasites & pathogens isn't too likely if you only handle him (or tend his cage) last. Sounds like he was their ONLY snake also, which makes him far less risky than a snake coming from a pet store or from someone just down-sizing, IMO.
You'll want to know what he was housed in (size of enclosure) IF he doesn't come with it. He probably does though, which would help for a smoother transition.
You might never be able to change his preference of eating mice...too bad we're not neighbors, I always have too many! As far as refusing f/t, the former owners many not have known or tried all the tricks we have up our sleeves, like blow drying, but no guarantee. Could be easy or a "royal pain".

Sometimes you can give a small live mouse appetizer, then chain-feed a f/t.
Not sure you'll ever need to "call his name" before handling?

But getting a snake's attention so they aren't startled, sure, that's a given. And massages? sure, why not?
From their description about possible finger-nipping, I have to wonder if he's been fed enough- that sounds like hunger to me, & it might not be so hard to transition to f/t (or even a rat) IF you scent the prey with some dirty (used) mouse bedding & warm the prey- ask your local pet store if they'd save you some.
Agree with you totally on the "bathing" question- & he might love a nice big humid hide instead- way more "secure". He probably "loved a bath" because his humidity was chronically too low.
I'd expect the sudden life changes (especially for an older snake) to unnerve him for a while, but he's probably 'do-able' if that's what you want- sounds like your heart's in it, but make sure the extra efforts will work for you- only you know the answer to that, & there's no guarantees.
