Am I understanding how this works? I was in Beta but had limited time to play. So if all your characters share the same bank and all crafting mats can be drawn from your character's inventory OR the bank then by definition all your characters harvest for one another as well. Is this correct? Kinda cool.

They can, as long you put your items in the bank for any one of your characters to take, which is really good if you make a dedicated-crafter character.

Or even just if you want to specialize in one element of crafting per character but can share resources with other characters specialized in other areas.

Will a purely dedicated crafter work long term? Aren't items' levels dependent on the crafters level? If a character truly only ever crafted how would he/she get high enough level to make really good stuff?

If you have a dedicated crafting character with all crafts maxed out, you can make any level gear you want. So, if you wanted to, you can make a level 10 item for your level 10 alternate character if you want. It just depends how many resources you used and how much you upgrade the item(s).

I thought it was dependent on the character's actual level and not their crafting level. I thought crafting level effected rate of drops from disassembly and success rates in crafting.

Please correct me if I'm wrong.

Anything you put in the bank can be used by any of your characters.

So you could have a crafting character and different alts to go out and collect materials for that crafter.

Just a couple of points to bear in mind - in order to use higher tier materials (for smithing/clothier/woodworking) and higher tier runes (enchanting) a higher level of solvents (alchemy) or to learn higher level recipes (provisioning) you need to spend skillpoints - so you need to accrue skillpoints on any crafting characters in order to have those to spend on doing the higher level stuff.

Crafting 'inspiration' is separate from character level but you still need to spend skillpoints on it so you still need to gain levels/find skyshards/complete quests to get those skillpoints to spend in crafting higher level stuff.

A level 1 character can craft level 50 gear, it just takes more materials. Of course, they wouldn't be able to use it, but they could still craft it for a friend/alt.