Upgrading to v4

I’m now ready to upgrade my current v3 SGP. One question: as long as I don’t exceed 3 installs, can I upgrade one laptop first but leave the others on v3 for the time being? I want to make sure it all works before upgrading the others.

Yes, absolutely. With a normal 3-instasll license you can install either v3 or v4 at any time going forward. You won’t be locked into v4 by doing so.