Just curious if it's okay to backup Rule Machine (4 or 5) apps (child apps) to my PC and to restore to a Hub other than the original. I assume I can't do this between hub versions, but is it okay to do it between for example two C7s with the same platforms?
Yes. When you restore it, it will ask you to map the devices, so you will need to have the same types of devices available on the other hub.
If they aren't available, it will create virtual devices with the same driver. These devices wouldn't work for anything, and would need to be replaced with real devices.