-Pretty much anything can be done by anyone save for more sexual content which needs to go to PM or simply not be done at all due to the way the site is funded. Heck, post count isn't necessarily required to get into things. You pretty much just join topics that are managed by a Gm, 99% of the time create a character and submit it, and after it's accepted start RP'ing.
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-There's places for both that are quite active. More sections are dedicated to more group based ones, but there's a pretty active 1x1 forum to itself.
-Not yet.

[url=http://www.roleplayerguild.com/topics/4958-a-new-users-guide-to-the-guild/ooc]This link should prove useful to you.[/url]

Feel free to dip your feet into the "Formatting Cheatsheet" at the bottom of the page.