You can go straight to Pro. It supports external MIDI instruments.
I think you can use the same eLicenser and, since you already have it you can get the Pro trial version!
Yes you can use this one. If you buy a new license of Cubase, you will get an USB-eLicenser with the box, and the license will be stored on it. So, copy all licenses to one USB-eLicenser.
I’m using Alt modifier a lot, which gives me an “alternative” tool. From my point of view it’s very smart, and most of the time I don’t need to switch the tool.