I can't answer all of your questions.
It would be best to have Springfield explain the safeties when their site loads for you. Basically, trigger and grip safety. There is an optional manual safety on some of the regular XD models. Exactly dimensions are also on their website.
There is no XDm Compact at the moment, but there is rumored to be one that will be released early next year. I'm looking forward to this myself.
If you want a sub compact, you will have to go with a regular XD model at the moment. That would be the XD9sc or XD40sc.
Good luck with your search.