Hi Stephen,
On the helpdesk license, I could install this on a laptop to be mobile
Yes, you can install RUT-Viewer and take the laptop with you anywhere where there's an Internet connection.
and then give clients the ability to install the server software
Yes.
and I can then connect to 1 client at a time. Is this correct?
Correct. Buying 1 Helpdesk license you can occupy 1 Internet-ID channel.