I think they look at the scores you send - in some of my interviews I was asked if I took the DAT multiple times but I only took it once so I cant tell you what their reaction would be to retakes
No, sorry. I only took it once as well. You can try doing a search though. I think the same question came up last year as well, and a few schools were mentioned.
I don't think the highest. I think they look at the last score which is basically reported on your AADSAS application. However, there is a chance that they ask about your scores on the first or second try too, if you have taken it multiple times. I guess it depends on the school.