It really depends on how much focus each thing takes. It's literally impossible to do any kind of multitasking without some loss of quality for each thing, but things that take less focus will obviously work better with multitasking
Yep, exactly this. I can watch a crime procedural while playing a JRPG, but if I want to watch The West Wing or play a particularly intense game I need to be focused on it exclusively.
One. I like to focus on what I'm doing at any given moment. The most I'll stretch this is playing an RPG while I listen to a podcast. I turn the sound down on the game, start the podcast, and grind in the RPG. Even in that instance, the RPG really is getting the barest amount of my attention.