The wiki is accurate as far as offenses, and punishments go. Pay attention to the sections called Reproval, and Shunning. It's rather dry, and doesn't really paint the full picture. JW Discipline
This was my experience. I was 14 when I was baptized. Once you're baptized, you're in the system… for life. You can try to get more responsibliity, but if you screw up, for the first time, there are consequences. It shouldn't be a decision left to a child. I did it because everyone said I should. The young people on my mother's side of the family always got baptized early. That side is a stalwart JW family, going back three generations. My great grandfather, a WWI vet, was converted at some point after the war. I like to think that the idea of a peaceful, and serene world appealed to him after some of the horrors he witnessed. He became a missionary, and died in Papua New Guinea. My uncles were Elders, all very well respected in the congregation. It was sort of assumed that my brother and I would follow suit, and take on a leadership role. My cousins, on my mother's side all excelled in later life. One is a full-time pioneer, and the other worked at Bethel in NY. It's a lot of pressure.
I slowly began to realize that their teachings weren't accurate, or reliable. That they were very controlling. They teach that the congregation, and your relationship with God should be stronger than your relationships with your family. All free thought is suppressed, and replaced with their teachings. They don't want you to go to College, because it can make you think in ways that are dangerous. Not only was my 'education' very lacking, but many innate coping mechanisms that healthy people develop, are absent in JWs. Very mundane decisions are made for you like, what position to sleep in, what to wear, appropriate hair styles and grooming, and how to speak. I realized it was bullshit, and rebelled using the typical tools available to an angsty teenager. All mostly minor infractions, drinking, weed, fooling around /w any girl I could, breaking curfew, and generally butting heads with my parents at every opportunity. Under normal circumstances, somewhat typical teenage behavior. As a baptized JW, they're all damnable offenses.
It was extremely difficult to extract myself, and even more difficult to recover from the emotional abuse, brain-washing, and resultant trust issues. The JW's are a very closed/tight-knit group, so everyone knows everyone else, and everyone is watching everyone for bad behavior. If you begin to stray, they try to 'encourage' you into coming back. They have their own phrases, and ways of speaking, that wouldn't make sense to an outsider. The 'Society/Governing Body' is faultless because their words are those of Jehovah, and as such their edicts are inviolable. Think a slightly less militant version of North Korea, where Kim Jong Un = Governing Body. When i was between 16 - 18, I gradually became less and less involved, until I moved out of my parent's house, (and the state) to start over, at 19. Had I remained, I almost certainly would have been disfellowshipped, because I had been both privately, and publicly reproved already.
So what's so bad about being disfellowshipped? I would have instantly been shunned by the vast majority of my family, and ALL of my so-called friends. My entire social network, and support system would have been ripped out from under me. Many disfellowshipped people have been so thoroughly brain-washed into believing that the JWs are the only 'Truth' and source of salvation, that when shunned, they feel they no longer have the love of their family, or the Light of God. They're on the outside, and everything they do means nothing because they're doomed. Because of this, many go to extremes of behavior, and are lost to drugs, alcohol, and suicide because they have no hope for the future. It's twisted, and cruel, and it very nearly killed me.
In real terms, to someone casually involved, they don't have much power. To someone with a very vested interest, they can literally destroy your whole life. It's taken me a long, long time to rebuild my life into something that makes me happy, and fulfilled. It's still difficult, though, 15 years later. Thankfully, my mother and father haven't severed ties with my brother and I. I've seen parents completely disown their children under the same circumstances.
I could be wrong, but it sounds like you (OP) got out in the earlier stages, and left in style. I've often fantasized of Disassociating myself, but it would be too hard to never speak to my already estranged family members. Congrats, OP, you made the best decision of your life! Don't look back.