If you do an FF9 solo, for goodness' sake use someone besides Zidane. Anyone, I don't care. Vivi sounds cool though and IIRC his avaiability is pretty excellent.
I can't say I found reinforcements that big a problem in XF? Unless you're spamming Turn Shift like mad you shouldn't be running out of resources due to them (except maybe trying to do 1-15 without Sanctify). And even if you do run low on resources you have several recourses, formation arts (physical dudes) and combination arts (magical dudes) are a pretty effective way to output damage without MP. (edit: MP Burst can also help, but it's gambly. It works better if you have a Magic Berry or two just in case, or some other method of regenerating MP to try for MP Burst again, such as the various "___ and Heal MP" skills.)
2-4 is a jerk, no question about it. Game does tell you that losing a PC is a loss condition though, it's in the condition screen (always check for "any ally falls in battle" vs. "all allies fall in battle"... latter is more common but more puzzly/trickier maps call for the former often enough). I had thought the game tells you you have to lower three enemies into critical, too? Could be wrong there. Regardless you know it now. It's still a nasty map, but yeah, what you have to do is critical three enemies then rush through the gate. I recommend getting as many people as possible near the gate before you trigger it to open. (The much-maligned Geomancer can let you sneak some people over there, and their armour resists the nasty elementalist offence!) For another protip, the reinforcements can cast Shut Out to stop you from escaping so either escape quickly or carry people with Dispel to deal with it.
Also Felius' Status Absorb lets you yoink away Misery from all your PCs, and either he/anyone he status absorbed can then use those Peppy Acorns (which I never knew about, shows how much Excavator I use probably; kinda cool though). If someone dies you can also revive them and they won't be miseried any more, though that's less elegant.