Quite a while, but keep a small squirt bottle of tank water near by and keep them moistened every so often.
Ideally, yes, especially if you intend on selling them...... very few people want just one polyp. I've got a couple zoas like that..... they kinda grow out in a circuit board pattern rather than in a cluster. Just use larger frag plugs (or small rock pieces) so you can get a few of them on at once.
And I second the wearing of protective gear (gloves, goggles/safety glasses, and dust mask). A very low percentage of paly/zoas are highly toxic, we just don't know which ones, and you can't tell just by looking at them.....google "palytoxin".
Some manly-men claim to have been fragging for years while bare-handed, without glasses, smoking a cig & eating a sandwich without any issues, but I see absolutely no sense in even taking the chance.