Getting a tag wrangling team set up would be a priority for me, as that would help with several of the tag-related issues (and I’d be happy to be on such a team!). I’d be in favor of letting those people both remove tags from games and delete tags completely. Also echoing Encorm re: tag suggestions. Basically, getting some systems in place so that tagging can be improved going forward, even if every tagging issue isn’t addressed right now.
Just looked through all of these; the one I personally care most about in the first category is #496 (automatically mark reviewed/rated games as played), and in the latter, #333 (easier adding of off-site reviews).
I like the general idea of #332 and #340, but since some people copy over their forum reviews to IFDB, this would end up duplicating reviews… (i.e., there might be an IFDB review of a game by someone and also an offsite link to the same review posted on the forum or elsewhere). That wouldn’t necessarily be a problem, but doesn’t seem ideal, either.