You should start working on learning riffs. You don't have to know many chords. Many of the best punk rock bands were formed after the guitarist learned his or her 3rd chord. I think it would be better to know many chords. Your riffs wouldn't have to get too complicated but you could distinguish your music more easily. Most chords you will probably play as a punk rocker will be 3 notes but still study more chords so that you can write better music. I would suggest going to different guitar tab websites and looking up guitar tabs so that you can expose yourself to more music. This will greatly help in the songwriting process and if you decide to switch to a different genre, you won't be too confused.
Ok I have written the riff below. It is part of a song i wrote called 'march of the dead'. it is about trends. It is kind of slow but not all punk is breakneck fast.
These are the 3 chords in the main riff. Practice changing the chords. I am not to hot with the sequence composer so when you practice this you can make up your own rhythms. Learn to play so you can do crazy stuff. Learn to jump around, lay in the floor, talk to your friend, headbang, and all sorts off craziness as you play this. If you can not put on a good show, then make sure you keep your day jog. 1/3 of being a good punk rocker is doing this. In a survey, more than 1/3 of people with ADD and/ or ADHD like this music and if you cannot keep their attention then you lose a good chunk of your audience. Do not think i am dissing you, your family, and your friends becasue i just said this. I have ADD, my brother has it, and my best friend has it. Believe me, if we have the attentions span to concentrate on you, then you are awesome.