I would also back up contacting the police justs because you were physically injured by them, and you really weren't doing anything wrong. i have no experience with this kind of environment so im not exactly sure on what to do.
you could try to take some martial arts classes just to make sure you know you can defend yourself, at least in hand to hand combat. i haven't been in a fight before but im a red belt in taekwondo, and now regretting that i quit and didnt get my black belt (one belt away, but i would have gone into a jr. black belt at the time) though i also study a lot of martial arts and since i dont do a lot of sports i guess i sort of teach myself what i didn't learn under a teacher. ...taekwondo, taekkyon, hapkido, taijitsu, wushu and more. i personally enjoy them all but just be sure never to use them offensively, starting the fight. Defending yourself is something i think is a great thing to know just in case. pressure points are fun. though i like to know them not to mess around with them, some i have an idea about that can paralyze arms and legs for few minutes.
i watched something on tv i think it was surviving disasters or something. pepper spray equals some type of alcohol and a hot pepper powder mix in a spray bottle. (what we learn on tv) Habanero all the way heard there one of the hottest.
i also agree with just try to ignore them and take action only if they come onto your property, i know loud music can be annoying, depending one what it is i listen to everthing including screamo so it might not bother me as much, but you might be able to block it out with your own music. um i thought i read rock would go into your nep window. security cameras there catch them in the act. im sure if any major damage is done to your collection we will all be here to help you get back on your feet.