1} Is there a way to switch your party members without having to go back to the Lounge each time? I'm open to solutions via console commands, since the Arbitrary Party Size Limit is something that annoys me in all games anyway, especially when you have to hoof it halfway across the game to get a specific character to chat with a specific NPC or use a specific skill.

2} Is there a way to remap the \ speedup key to something more accessible, like the middle mouse button?

3} Are there generally any extra content/QoL mods you'd recommend?

Not without cheating. But apparently there's a developer menu with debug options that lets you do it, check this thread:

http://www.gog.com/en/forum/anachronox/is_there_a_quick_way_to_change_party_members

Unfortunatley it gives you access to all party members from the start so it's really not a good idea unless you've already finished the game once. Probably... check the default.cfg file inside the configs folder. There is likely a list of control bindings including the \ key. Not sure if it will accept middle mouse button, but a different keyboard button should be easy enough. I don't know of any mods for Anachronox. Anyone else know of some?