I'm sorry Francois! I didn't see this "new message flag" until this morning. I probably looked at your original message and then got distracted and didn't answer it.

We are planning to have a shared setup hosted remotely.
I currently own a "basic" licence which I would like to upgrade to "personal internet".
So:
1. After I upgrade, my understanding is that my 2 fellow astro-imagers with whom I'll be sharing the rig will be able to connect to the web browser from anywhere, just like I'll be doing. Is that correct?

Yes, that's right. And each of you can have your own account with your own image, log, and plan folders.

2. We need to have ACP running on the PC in the observatory whilst I currently have it installed on my personal laptop. Can I simply install ACP on that new PC and use the same licence number to activate it?

Yes, as long as you are only using ACP on one computer and observatory. If you want to continue using your laptop with current observatory then you will need a second license for the new observatory. One license per observatory.