Considering in the Q&A he did mention 13 (though I do think he was throwing numbers around) the possibility of a 1 and done season 4 are quite low.
It all depends on episode 12 really, language would suggest it is the last "normal" episode we are getting. After that who knows, but I would guess at least two, one to tie up loose ends, possibly with a few ground laying choices and then one to actually end it that is just on rails. How big they become and if they need to be split for reasons is down to DPC
Yeah, it really depends on how huge he's going to make episode 12. I think I don't exaggerate if the Dorm party was about 2 to 3 times the size as the 2nd largest freeroam of season 2 (probably the HOT party when it comes to the amount of objectives including optional).
When it comes to season 3 so far, to me it felt like the Halloween party was about as big/long as the panty party (if you decide to do everything). I'm pretty sure DPC will try to outdo himself again for episode 12, so I won't be that surprised if he's going to make the huge freeroam of this episode at least 1.5 times the size of the halloween party/panty party. In that massive freeroam MC can tie up a lot of loose ends with love interests if you haven't/couldn't do so before it.
If DPC is really lazy, he could even use this freeroam to finish all the current open "main" storylines in one go:
- Vinny, Buddy and/or other people crash the party in search for Quinn and/or Riona
- Stephen crashes the party in search for Quinn (and maybe Mona if she decides to return and go against him) if she decides to talk on him in hoping to redeem herself after the situation with Buddy and Riona
- Magnar and his supporters crash the party hoping to see the big brawl (which probably won't happen) between the frats, only to find out the frats found out the truth that Magnar was behind it all and team up against him.