I'm going with it being a flying type. Sylv as the root word leads to sky/wind fairies that are female. Some kind of bird as well.

I could see only female Eevees turning into this and males turning into one that looks a little more masculine, maybe a ground or rock type.

Your logic makes sense because the French name of Sylveon is "Nymphali", nymphs are female nature deities with Celestial Nymphs being of the five kinds (the others being Water Nymphs, Land Nymphs, Plant Nymphs and Underworld Nymphs).

Yes, but Clefairy is a normal type, and pink.

How many variations of Eevee-lution stat breakdowns are left?

Flying was one of my three guesses, though it wasn't my first choice. Now that the name's revealed, I agree that Flying seems likely.

I guess a very equal mixed attacker to go opposite Umbreon who is well rounded tank defense wise. Flareon can be fairly mixed but more along the lines of attack and sp att reaching 350 each.