I can hop in on some of these questions.
If editing an older tier, to now require an address, would automatically make their address visible.
No, the patron needs to specifically give their address to you, so while you can make the address required, that will only make it required going forward. However, you could do this and then ask existing patrons to update their address if they want what you’re interested in sending them. I tested this out and realized that the address prompt doesn’t show up on /pledges, but if the patron edits their pledge they can add an address there. I’ve sent this feedback to the right product team as well to see if they can give a prompt to add an address in this case, as you recommended here.
As of a couple weeks ago, we started saving addresses on the patron side, so you won’t need to add it separately for each creator. That was the case for a long time, so you may remember it being that way. It’s better now!
Hope this helps.