Have to say that while fire is one of the most commonly resisted damage type (after poison IIRC), but that doesn't mean it's commonly resisted relatively to how many beings there is in the game.
Way of the Ascendant Dragon will remedy to that, anyway.
I agree with this, if there isn't something specific the player want to use, DEX and WIS are always welcome for a Monk. And multiclassing costs more to Monks than most other classes, so if you're doing it it has to be worth the trade-off.
Hard disagree on this, though. Monks have utility, even if some subclasses have more than others.
Personally I don't think Mobile is that great for Monks, either.
Regardless, Ascendant Dragon Monk is one of the most straightforward builds unless you're going for a gimmick.
Just use a staff with two hands for your Attack action until your Martial Art die catch up with the staff's two-handed damage, use the breaths as appropriate, and keep both DEX and WIS as high as possible, and it'll do great.