I just started trying multiplayer, and I'm confused. Is there a single pool of items to use in both MP and campaign? Is it possible to accidentally sell my MP items in campaign mode or vice versa? I can see both parties in both modes, does that mean I can use either party in either mode? If I give an item that was on my MP party to my campaign party, will it still be on my MP party when I go back to MP?
Items share a pool, you can use either party in any mode (though they autolevel to 18 in mp - no matter their actual sp level). MP party loadouts are different than SP ones, so it'll stay there. There's a new filter added this latest build that uses "unused items" or some such so you can check which items are equipped by any party to avoid accidental selling.