Garageband vs full version

Can I update from the Garageband account if and when I get Logic Pro X? If not will the regular account work for Garageband as well? Thanks!

The full version also can work the same easy way as MIDI Guitar for Garageband. In the full version you can choose “virtual midi” for output in the interface section of the standalone: that basically mimics the use of MG for Garageband.
We can upgrade MIDI Guitar for Garageband owners, but it is not cheaper in the end and more hassle than buying the full version straightaway.