Gonna just run with Nama's list. Trying to make other arguments amongst everything here is just headache-inducing.
Presence of SRPG elements (movement, AoEs): If I could just decide any one aspect on this game now, I'd make it an SRPG. We're looking for lots of characters? Perfect. Forced randoms with the option of grinding? Disgaea-style level selections. Honestly, this is pretty much the ideal thing for me, and I really can't see any benefit of things like BoFV-style over this.
Impact of speed stat on actual speed: Should definitely be simple, yeah. I'd much rather go with just "Speed = Turn Order" - maybe make the average 100 just to really simplify things. >_>
Resource limits: If each battle were done separately, I'd make them individually challenging with an auto-regen of some kind after battles. I'm guessing items fall under this, which is a whole different story and should probably wait for a different topic, honestly.
Expectation of PC durability: NOT capable of being killed in one hit. I hate those fights that are just "Revive, Attack, Revive, Attack, Revive, etc." Otherwise, ehh, not that important.
Scale of battles: Uhh, what? I'm not really sure what this means, honestly. Generic battles should be quite challenging, a lot of variety, but with less tricks/interesting strategies than the bosses?
Presence and use of switching alongside active party size: Yup, sure. I like Djinn's idea of moving out of enemy range far enough to switch, but as for how to encourage this... Another one that'll take a little more work.
Presence and effect of combo system: Ehh. Irrelevant to me.
Presence or absence of combo attacks: If they're original, then sure. If they're pretty generic, then forget it. I hated Disgaea's combo system, and would much prefer something different depending on who you use.
As for the characters included, I'd say each person should pick a few characters. Maybe 3 per person, since that'd be a large cast with a lot of variety, each team of 3 would be designed to have synergy, and it would be a relatively small amount of work for each person. That said, I'm guessing some people don't like the idea of having 35-45 characters.
And Dude, I'd honestly not mind a game that's almost entirely sidequest. But, yeah, that depends on how the skills are obtained - if they're, say, gained through fighting a certain number of battles with a certain character present, then they'd not need any sidequest to obtain them. And, again, I think this is an issue for a different topic.