Hi, I am licensed at v2 on LRTimelapse. If I upgrade to v4, can I move my license to my Mac?

Yes, you can use any license on mac or pc.

Can I uninstall on one machine and reinstall on another? I'm assuming this should be okay. Can't get my visual previews to work on my laptop so am going to try it on my desktop machine with more ram and GPU.

Yes, you can deactivate the license via the info/licensing dialog. Then activate on another machine, just use the license key from the email that you received.