Note: ADISC does NOT allow personal ads. This includes "looking for ____" or "anyone in ____" type introduction posts. To write a good introduction, focus on explaining who you are, NOT what you are looking for. The goal should be to help other people get to know you a bit.
Don't worry if you come and go. On most forums I have ever been on for anything (all except this one) I have either gotten bored of them in which case I pop back occasionally or didn't like the people in which case I left and didn't come back. I have even had one or two periods where I didn't do much on here back around May and June. Some people aren't forum people.
Don't worry about it. I have an idea, find the one thread that most interests you in a day, and post to it, saying as much or as little as you want. Once you are doing that without thinking, try moving up to two threads. Slowly build it up to a point you are comfortable with. I know a lot of people here either post loads and loads or not very often at all, and there is nothing wrong with that. Just do what is comfortable.