Is there a shower drain pipe in this picture?
A shower drain needs a trap, so check under the cap on the left to see if there's a trap or a straight drain. If it's straight, then your assumptions are likely right that it's a toilet and the other one is a clean-out (fix that cap, you don't want sewer gases getting it). If you don't have a shower drain here, then I'm guessing it's only roughed in for a half bath.

I don't imagine the 2" would be anything other than a vanity drain.

With the "vent," I'm left wondering if it's really a drain since I see a clean-out installed on it. I'd recommend tracing that line up the walls, as best you can, to verify it really is a vent.

As for where the horizontal line is going to the left, perhaps a washer dryer, or perhaps the plumber screwed up the T and it should be pointing to the right for the sink. It's hard to tell from here.