Thanks, tdjcbe. I'll re-set to 5, I think. Nothing in the site yet, so not a problem.
Hi andrea_r, not so much problems, just I had a choice and wanted to make sure I started off on the right footing, rather than build a site then disclose that I'd chosen the wrong MySQL version to do it with. Personally, as a Luddite I'd have prefereed they just gave me a couple of MySQL's, rather than asking me to have to make a choice. But pleased to go with the principle that newer/latest is porbably the best bet.
WPMU installed okay - though I haven't done much with it yet to test every angle.
B.
While we're here, I'm thinking of learning php for WordPress / MU. Is there a best bet for that type or teaching that would be best recommended? - I mean for being able to do the coding to display posts, excerpts, and all the derivatives of those tasks, etc.