Just out of curiosity, would like to know who will review/accept tag wiki/excerpts edits and reputation required to review tag edits.
That privilege is reached at 1500 reputation (on non-beta sites, it's 5000):
Finding tag wikis to vote on
Users with the privilege to vote on tag wikis will start seeing them appear randomly between other posts in the Suggested Edits review task. You can also visit the tag wiki page itself and click on the edit links (similar to a regular post with a suggested edit pending on it) to view the suggestion and vote on it from there.
Tag definitions/creations are only necessary if they have five or more questions. The reason being that there are plenty of users/questions/topics that come here for one answer, and never come back. Creating a tag for one question has potential to create unnecessary bloat.