I just use
http://wowpedia.org/API_GetItemCount in MiniLoot.
Not sure, but it should update properly when crafting like that, though does the reagents count as bank? I hope so, in that case it'd be awesome for us. :P
Yes strictly speaking you don't need to visit the bank, it's kind of like your hidden bags that are always with you but inaccessible when not speaking to the banker.