You are correct on all your hunches or research. 

As mentioned, the activations (SF2, SF3, and/or RTK) are lifetime. But if you wanted to move them to a different 3000 you can. Or if you buy a 6000 you can move them up for a small fee. 

And for any of those higher accuracy signals you do need to buy a period of time subscription for that signal once you do have a lifetime activation on it.