For the shoes issue, I have heard of people bringing a pair of nice flats to change into during the tour, but that seems risky to me - what if they don't have a place to leave your heels? Do you really have time to change? Do you really want to attract attention to yourself?
So, bottom line, I would wear something that you can walk around in. If you have experience walking in heels, go for it...if you don't, that's something to keep in mind BEFORE you break your ankle on the ice in Minnesota in the winter...just as you probably ought to think ahead and tailor the weight of your outfit/coat to the weather.
Furthermore, the MOST important thing is to wear something that you can feel confident in. You should not be thinking about your shoes on interview day. Your interviewer should also not be thinking about your shoes. Unless perhaps your shoes want to go to med school, and are really just using you as a convenient ride to the top (but probably not). So if you are inexperienced and uncomfortable in heels, either practice in them or avoid them.
My personal plan is to find some professional shoes with a nice shape and a
slight platform heel - 1 or 1.5in - but not a traditional 'heel' shape.
I am very uncomfortable in heels though, and actually look like I am on the verge of breaking 2 ankles and a knee at all times while attempting to walk in them. Seriously, I tried them on in a store once and my mom took a video of me to send to her friends so they could die laughing.
As for the dress/skirt thing: honestly, I would go with a suit look. The other looks nice, but there is more variation and therefore, inevitably, less consensus on what the 'right' look is. If there's a look you KNOW is acceptable to everyone vs a look that is acceptable to most, awesome! to some, and no. to others, why take that risk? PLUS, then you have to worry about which hose/leggings to wear under it (bare legs are usually seen as unprofessional), it's harder to match shoes, and you're almost condemned to wearing heels.
seems like extra hassle for no guaranteed benefit...other than looking kick-ass! And hey, if that makes you interview better, go for it. If you are unsure about anything, it might hamper your mojo, so go conservative.
Your clothes shouldn't be projecting your personality on interview day, you should be. Pick the outfit that allows you to do that to the fullest without distractions (visually or comfort-wise) or sending its own signals.
Then again, you pick your clothes, so if you are confident in your ability to project the image you want, go for it! 
