Can I install SS10 alongside SS4? How would the licensing work?

Yes, two questions in one because (for me) they go together.

We would like to research the upgrade of our SS4 software to the SS10 versions, while we wait on our larger clients to upgrade to CONNECT. By research, I mean, install SS10 on one or two computers to see if there are any issues, before we migrate the entire office over.

Our current licensing is over Select Server. I know that SS10 uses Client Connection licensing instead. How would we license that one copy of SS10 in order to test it out?

Is it possible to install SS10 onto a computer that already has (and needs to keep) SS4? In case there ARE issues, I don't want to lose the ability to do my work by giving up the software that I know works. Or will SS10 overwrite SS4, no matter what I do?

Please be as thorough as possible with your answers. I am going to have to pass all this information on to IT and our Software manager, so overly-detailed explanations will be appreciated.
Thank you!

MaryB