I've been playing since last Tuesday and just hit 41 Alliance side.

1. Mob spawn respawn rates are not unmanageably high but it does make kill quests easier.
2. Bags are reasonably rare however by 42 I'm rocking entirely 12 slots from various sources, none purchased. I had full six slots by the end of azuremyst (10).
3. Mobs pat pretty good in dungeons. Some things are a bit weird e.g mob flee speed is super fast which made SM armoury and Cath interesting but it was ok. Deadmines has some screwy pathig issues but it was ok. Every vanilla dungeon I've done so far has had mobs working correctly as well as some a bit off. However it's all doable.
4. I chose skinning and mining to stockpile resources to switch to leatherworking and hammer smith later on. The mining nodes don't seem overly frequent however Jangolode mine in Westfall was a bit over saturated. Haven't seen issues elsewhere in fact I've had to specifically seek out nodes to level effectively.
5. I've had an expected number of greens in the world drop and the only dungeon I've experienced with elevated blue drops was gnomer. We had two of the 2h drop and 2 of the 1h mace drop. Doesn't seem overly elevated but that is a bit high. And yes the rare spawn mobs in dungeons appear to be auto spawn in vanilla. TBH it doesn't phase me because 1-58 is a grind and spicy loot makes us all happy on the way.