I would choose option #1 as well.
UE cases are $70 a set aren't they? So $140 for 2, that's the same price as the FLM hybrids, but the hybrids have aluminum bulks built in.
Stock diffs gears may last a while with al cases, but with your setup they'll always be a weak spot, so 1/8th diffs may be less hassle in the long run.
I suppose if you don't want to spend $270 in one go (again) you could use the UE cases with stock diffs for now and get the HB diffs later on, but I would prefer the hybrids if it was me.
or, option #3: wait a month or so until traxxas releases the new emaxx diffs. much cheaper, and you can sell the diffs you have. (the big question is if they're really as tough as traxxas touts )