Sick of old forum, considering starting a new one with Discourse

[Falco]

@gdelprete

5. can editing a post be disabled, or at least limited to a very short timeframe?

post edit time limit site setting. Use 0 to disable.

@gdelprete

4. can users be blocked for a period of time?

Yes.

@gdelprete

1. for clarity, we need to provide users of the old forum with the ability to subscribe to the new one while keeping their username; what would be the best way to achieve this? Can it be achieved at all if I enable social log in?

I don’t follow. You can choose the username. Just choose the same when creating the account.