Yeah, well just because it's a prequel type story doesn't mean we have to stick to the actual timeline of members joining the forums. The problem with only using a few people from after the new forum was made is that there is a very small minority of people still active on the forums who were part of the old forums. As such, it may be better to use primarily characters still active now (this, I think, will have a greater appeal to the reader).
Personally, I think Ridder's idea for Main and Supporting Characters is pretty good. (And I think Demonik, being a former global mod, should appear in one scene as a wise old sage who imparts some advice to the main characters.

) As for foes, ourselves is not a bad idea (internal strife in forming the forums, and whatever), but I also think that using some of the forum's notorious rulebreakers as foes might work (not those that brando used in Runouw's Forum, but ones like Linkdroid and Raymond maybe).