You should talk to both lowerclassmen and upperclassmen, if at all possible. Get a feel for how they like the school, pluses and minuses, etc.
Specific things to ask:
- Quality of clinical rotations
- Grades - how are they decided, when is it P/F (is it TRULY P/F), are rankings kept, etc
- How supportive the school is with the residency application process.
- How fourth year is structured (when does it start, how much vacation do you have, do you have to do rotations during interview season, how much is required, etc)
- How much dedicated study time is there for Step 1
And, since you're going in late March, asking for the match list isn't a bad idea, keeping in mind that there isn't a whole lot you can interpret from it. In general, though, you can see if anyone is going to an area you might want to go for residency, how diverse the class is in terms of specialties (is everyone going into Family or Derm, or is there a good mix?), etc