For the #3 the actions should be like this:
“Add customer tag” => “Wait: 3 days” => “Remove customer tag”
For the #2 – simply schedule your Flow more often, say once per hour and then regulate the frequency by setting the “wait” parameter.
Basically, if a customer was sent e-mail they keep the tag for 3 days and does not get any new e-mails, then tag’s removed…
Say, you have 500 e-mail targets. With runs scheduled every 10 minutes, they will be processed within an hour and will sit with a tag for next 3 days. Then tag removed and they are ready for new e-mails.
However, while this will work, it’s probably not the most efficient way to do it.