So, quick update on how things went:
After losing 17% level exp (total) so far (I really hate Foundation...), I went for Sturdy Companion next. Seems to be helping. I really should have parsed those on Beta, but it was a really bad Beta for me, as I've attested to other places.
I was going to just stick with Rank 1 of Force of Elements, just so I could get used to working in into place on my hotbuttons, but I broke down and bought all 3 ranks. I really like this AA. It doesn't add that much DPS, but it's a very nice, completely mana-free, chunk of DPS. And if you're burning, say, First Spire or 7th or have a Bard in group, it's a nice, free, between spells 3k nuke crit. It's really very nice.
Now we just need a functioning Mana Regen spell because, oh god, I feel like a newbie again. New RmS timer just eats your mana alive.
On spell slots, until I get Thaumatize, I really don't need any extra. I bought the Aspect AA just on a whim (it's 3 AAs and UF is actually solid AA exp when you're chain dying) and that's really the only thing taking up a regular spell slot that I flip in and out. I'd have liked it to last 2 minutes, but it's still decent. I'll buy the new spells slots (and fix my UI files, lol) when I get the mana regen, probably here in a week or so, but for the moment, it's just not really pressing. It's no different than all the pet buffs I've flipped in for years.