You don’t need a valid PAT to browse the results of a previous analysis. But you’ll need one if you want SonarCloud to interact with Azure Devops. E.G.*, if you want to onboard new project or decorate PRs.
Ehm… maybe? It’s not clear to me what the conditions would be - I’m not an Azure expert - so it’s difficult to say. You could certainly test it, with the understanding that if things start to go sideways you would need to roll back.