Regarding Admins and Mods, the most important tool of Admin is the ability to block users and IPs. As we become more and more popular, the likely hood of spam and vandalism becomes more likely. (The first person to use the word "DESU" more than once will be subject to termination by an SCP of my choice!).
After that, I propose that Admins be made a "supreme court" of judgment on issues. Such as that of SCP-000. A majority decision of half of admin +1 will be a final, undisputed judgment.
Admin can also great the highest level of nesting in the forum, beyond just the "general, help?, and Creepy-Pasta" forums
As for Mods, consider them Admin in training. Once the consensus of admin agree that a mod has shown experience and consistent quality writing, a mod maybe promoted to Admin status.
At the same time, any user that shows the same may be promoted to moderator and so on.