I am not from Laminar Research; just a flight simmer from downunder.
I am not a Mac user but what I do know is what you will pay for a mid-range mac system will purchase a top of the range windows based system. Many experienced and recognised flight simmers and information providers are using windows based purpose built systems. A windows based system will allow individual components of your system to be upgraded, as and when you deem they need upgrading, far easier.
What you need to ensure is your new system has adequate cooling. X-Plane 11 more so than X-Plane 10 is resource hungry and generates heat. So you need good cooling for your CPU and GPU. If you don't then you may have a system crash where the screen will go blue and will not be usable until everything has cooled.
X-plane 10 is a totally different package to X-Plane 11. They don't mix and match so no point in trying to integrate. You can run both systems on the same drive/machine.
My following comments are based on the fact you are running a genuine Laminar Research version of X-Plane and not steam. Steam is a 3rd party hybrid that installs differently to the laminar version.
XP10 and XP11 can be installed on as many computers as you want but can only run one legal copy of that version at any one time. If you have a digital download then you have to be connected to the internet at all times as the software will perform a silent background check on the legality of your version. With a disc version you need disc one in your dvd drive at all times.
If you have installed XP correctly ie on the desktop or into a dedicated directory or even a dedicated drive all you need to do is delete the software as you would for a file or program. If you want to transfer XP10 to your new system then find a storage device (USB stick or portable drive) and just cut and paste and then cut and paste onto your drive of choice.
If your version is a digital download then reinstall your files and provide the 24 digit product key. For a disc version just reinstall the discs in the directory of choice and then insert disc 1 to run the software.
Hope this helps. Any further queries send me a personal message.
Good luck with your purchase.