My biggest advice (and it's probably controversial) is don't disclose to your flatmates. Not for a while. It can be a good thing but you also run the risk of people who don't know you and aren't invested in you feeling like they don't want to deal with your problems and ending up isolating yourself. Don't feel that just because you live with someone they need to know what's going on for you, if you wouldn't disclose to everyone you know in your general life, treat flatmates the same.
Try and look at uni as a fresh start, of course moving doesn't mean you're going to suddenly overcome your problems but give things a go and try not to assume there will be problems where there hasn't been one yet. Social situations can be tough but if you try and throw yourself in the deep end at first you might be able to give yourself more confidence to keep trying things. In the next few months you can try and put yourself in uncomfortable situations to show yourself that you can do it and get through it.
Don't rely too heavily on alcohol (assuming you will be drinking). It's normal to drink and to be honest it's normal to drink heavily at first but try and be self aware, if you're starting to drink just because you can't handle the situation you're in then it's time to call it and either remove yourself from the situation or force yourself to deal without alcohol for a short period.
There will be masses of things going on in the first few weeks, try and get involved where you can but practice self care too so it doesn't get too much. If you need a night off to have some quiet time alone then take one, better to attend half the nights and look like you're enjoying yourself than attend all of them and burn out and look miserable. Take care of yourself in other ways, get regular exercise, eat well and try and get enough sleep. Try and make sure that the stresses of your course don't build up, keep on top of your work and coursework and speak to someone if you need to.
You can still get a lot of family support from a distance, between texting and skype it's pretty easy to keep in touch now. It's probably worth working on dealing with panic attacks alone if you haven't already so that you don't end up with someone panicking and calling an ambulance when they find you struggling to breath one night.
Also: might be worth contacting your university disability department even if you're choosing not to apply as a disabled student just to touch base in case you need any additional support further down the line and register with a local GP asap so you've got that line of support as well.