You won't go to prison for this, unless there is serious injury. It sounds like there isn't so don't worry about prison. You will not be able to rely on the defence of intoxication, as your intoxication was voluntary, but you can use it in mitigation. Kiki frog is right - you'll probably get a community order and have to pay for any damage, plus a fine and court costs. If you are unemployed your income will be treated as £100 and that will likely be your fine. Plus you might have to complete an alcohol awareness course.
A solicitor would cost between £100-200 for a mags court case. The initial interview is usually free. I would strongly recommend that you get a solicitor. Dress in smart clothes - if you don't have a suit wear a smart shirt, smart trousers and black shoes (the first impression of the judge can make all the difference, especially in mags courts). Go into court with your head down and start by pleading guilty straight away - this will lower your sentence. Then explain that you take full responsibility for your actions and apologise to everybody (victims, police, court itself). This will go down well. Also suggest that you will comply with any order made (eg. alcohol awareness).
The most important thing to do is never get drunk and get silly again. I am a year older than you and, like you I used to do stupid things when I'd had a drink. When I was 18 I got very drunk and committed a rather serious motoring offence. I did exactly what I advised you to do, did my alcohol awareness course and got my head down in school afterwards. Now I'm in my third year of a law degree. My conviction turned out to be the best thing that ever happened to me - make it your wake up call too.