First three are fine with me without changes, but I need more details on the specific implementation of #4, and especially regarding false positives, before I can comment on that one.
Maybe we could have a trial period of #4 that merely displays a banner next to flagged posts, notifying folks that the account is suspected of spam, until it has been sufficiently vetted to reliably prevent false positives. The banner could also ask folks to confirm whether or not it really is spam.
Yeah, I wanted to implement HDMI on an FPGA dev board last year until I found out that I literally couldn't without getting that license.