Difference among Qsys Sim model, test-bench Qsys sys and test-bench Sim model

I'm confused about the purposes of different models that are offered during the generation process. In 'Generation' window you can have:
1) Simulation model
2) Test-bench Qsys system
3) Test-bench simulation model
4) Synthesis files (which I understand its purpose)

My understanding is that (2) is a wrapper system that contains the Qsys system to be tested, it also contains BFMs that are connected to the top-level interfaces of the system to be tested. By writing another HDL file that drives the top-level interfaces, I can check the behaviour of the system.

Q1: If the above is correct, now I want to do that in ModelSim, my guess is that having (2) alone is not enough, I also need (3) so that (2) can be simulated in ModelSim, is that correct?

Q2: If my guess in Q1 is correct, then in what situation I may want to generate (2) alone without generating (3)? (I think this is explained in "Qsys System Design Tutorial" but I didn't quite follow it..)

Q3: Is (1) a subset of (2)+(3)? My understanding is that (2)+(3) = (1)+(BFMs simulation model), is that correct?

Q4: If I just want to test/simulate my Qsys system using standard BFMs in ModelSim, it is OK to unclick (1) and only use (2)+(3), is that correct?