Hello! Yes, many people speak English. As far as tours, there are several self-guided tours that you can download on the internet. I did not see any guided tours beyond those that were prearranged with a professional tour company. We really enjoyed our self-guided tour.

When we visited I wore sandals as it was really hot out and my cousin wore trainers. It began raining and we were both slipping on the marble floors. So regardless of the shoe, just make sure it’s got a good grip on the sole. Cause there is a lot of marble and even without the rain we slipped a few times and so did many other people.

indeed that is correct, in fact it's basically all Roman architecture as Hadrians temple, the amphitheatre and terraced houses can vouch for.

I don't think you can visit at night. I didn't see any lights there! We visited during the day. I don't think the staff work at night either so you can't buy entry tickets.