Welcome to the forum :3
1. Use [img]url for the picture here[/img]
is [img] http://i1298.photobucket.com/albums/...ps1f2cdb88.gif [/img] with no spaces.
2. That's part of being a premium member. If you donate $10 to help keep the forum running then you get to change your user title (the little thing under your name) and your main shows up all fancy-like next to your posts. You can read more here.
3. You can edit your signature from the settings menu at the top right of the page, then edit signature on the left about half way down. You put pictures in it in the same was as I posted above, with a maximum size of 700x250 pixels. As for requests, we have a graphics chat subforum for that kind of thing, though I think you'd be hard pressed to find someone actively taking requests at the moment. Plus there's always deviantart, which has about a million artists who have posted signatures they are happy for people to use. (A million may be hyperbole)
4. I can believe that, but I didn't know it. I've been here for just over 5 years and am still pretty happy.
Pretty much anything else you might want to know is contained in the stickied threads in Technical Support or News & Announcements, including how to donate and what other effects it has.