First, regarding the 'define alcoholic' subject - I think the literal definition makes most regular drinkers 'alcoholics', in my mind - the real line between drinking too much, and being an actual alcoholic is morning (and to a less extent, day) drinking.. Even when i am drinking quit a lot (say a third to a half of a bottle of whisky each night), so long as I don't start drinking each day until after work / after 6pm - then I'm not too concerned with it, I think when you start drinking when you wake up and continue drinking until you fall asleep, then repeat.. That said - heavy drinking every single night still takes its toll on how you feel during the day, not too mention - it can still cause serious liver damage.
Anyway - regarding tips for quitting / tapering / cutting back. On one hand, I'm a current heroin addict, so maybe my advice isn't great, on the other hand - I've quit many other addictions; meth, weed, gambling (all these things I've quit for 5 years or more). And I've also quit cigarettes, heroin, alcohol each for various amounts of time, including a good 18 month hiatus from everything, so I guess I've had some experience here and there with putting a stop to an addiction (not taking it up again is just as hard, if not harder).
Anyway - I'll just offer a couple pieces of practical advice that have served me well on occasion:
Asking for help / confessing; I've found that living a double life and digging a huge hole by lying to everyone you know, especially your parents, family, loved ones and close friends - does the most damage. Sometimes it's easy to fall into a trap of thinking you don't want to damage your relationships and/or let down the people who care about you (perhaps they think you've been doing better and you don't want them to think otherwise), perhaps you find it humiliating, or whatever - the reality is, addicts often lie about their addictions, for various reasons. Sometimes the lie is outright - we completely deny it, our family, friends etc may not even know anything, we may have kept it all utterly secret - in which case, they know something is up, but they don't really know what, they just know things aren't going well for you.. Then there's the lie about how far into it you are, perhaps your friends/family were aware of an issue 12 months ago, when you went to rehab or something, but they think you've been doing well ever since, but in reality, you've fallen back just as hard as you were ever into it to begin with, and you don't want them to think otherwise.
Anyway.. you get the point.. addicts lie and maintaining the lie makes it very difficult to quit the addiction, because you're the only one who knows about it. So, one really effective method is to tell everyone that you can (within reason; don't tell your boss if it will get you fired; and in some cases, telling your family may not be a realistic option - some peoples families may literally disown them). But tell everyone you can - just be brutally honest about your life and ask for help, where appropriate. Then - importantly, keep people informed. It's no good telling everyone, getting clean for a week or so, then picking up the habit again, but falling back into the lies. It will be really hard, this bit. because if you tell everyone, ask for help, get help, get clean, then fall right back into the shit again, you'll feel like a real fucking loser - like you've let people down and it may be really humiliating, but - nevertheless, let everyone know where you're at; how it's going.
People WILL get sick of your shit, something you'll find is that people actively DON'T want to know how bad things are, they don't want your problem to be their problem, people are happy to listen to your bullshit lies and pretend to believe them, convince themselves of them, because it's easier than dealing with an addicts shit. By telling people the truth, you inevitably suck them into your shit. To begin with, people may even help you out financially - bail you out of debts, buy you food, etc. But - by the 10th time you fuck up and they start to learn that DESPITE ALL THE HELP they've given you, you still keep throwing it in their face by continuing to fuck up.. this shit starts to grate, people will stop offering you financial aid.. that's ok though. Once you start drawing in all the people you care about, into your world, you will after a while, finding it much harder to keep being an addict - basically - you'll want to either go back to lying about your addiction, or stop being an addict, because continually hurting people you care about, by constantly fucking up, really does fuck with your head.
The other thing, and this is quit a practical thing; try and limit your access to money.In the past, particularly as a gambling addict, I've had both my mum, as well as my girlfriend on other occasions, take complete control of my bank account(s) and cards, I'll have no direct access to my own money. One thing you may want to do for convenience is when you get paid, by a gift-card for a grocery store, that way, if you bust all your money, you'll still have money for food (and smokes if you smoke). This can be a huge help.. Similarly - purchase gift cards for anything else you may need money for down the track, at a point where you'd usually have blown it all on your addiction.
Anyway.. honesty.. that's what I've found helps the most.. makes things real.
Also - you're still really fucking young. I know that list you put forth of shit you've done, been addicted too, etc probably seems really huge to you now.. And, in a way it is, you're definitely heading down a dark path, no doubt. But honestly - you've still only just started to scratch the surface of where addiction can take you. You're basically just at the tail end of the 'heavy' experimental phase. You can still turn shit around and have your whole life ahead of you. If you fix shit now, then you've lost nothing. You're practically still a kid / teenager. So, you haven't done any permanent damage to your body and you can still recover fully psychologically too.. Once you get hooked on something for 10+ years, then it's a whole other story, even if you quit, you'll probably never truly get it you of your mind. But you, you can quit now and in a few years, it will just be a distant memory of some stupid shit you done as a kid.