Can I use a licenser that was once used for cubase?
Yes. You can move licences onto a licencer you already have using the eLicenser Control Panel
If I buy an eLicenser, can I transfer my softLicense to it yet? I’d like to check how Dorico works on my Mac laptop, but I installed it on my Win 7 desktop since that is the machine I will use for most of my work.
Yes, you can transfer your current license to the USB-eLicenser. What you cannot (yet) do is transfer the license back from your USB-eLicenser back to a Soft-eLicenser on another computer.
I have succesfully download my Dorico license onto an existing e-licenser which has on it licences from other vendors - example, all my Vienna Symphonic Orchestra Licences, with Dorico, being my first Steinberg license, now on the same e-licenser.
Everything is up and running, with Dorico now fully installed, and doing what I would expect.