Today I added the last bit to my setup - and to my personal convenience. I bought an old iMac 27“ from late 2009. This machine is still awesome. The specs: 16GB, 512GB SSD + 1TB HDD, ATI 4850 plus wireless keyboard, Magic Mouse (which I don’t use) and another Trackpad 1. Sierra was preinstalled. This machine is huge and the display only has one pixel failure - I can live with that. Most remarkable: it was cheap though I had to drive 1 hour one way (about 200km) to get to the seller in a very rural area…
After installing all the apps I previously purchased on my MBP I also installed and copied the other stuff - which went flawlessly good and fast. No issues so far.
I cannot believe that this computer is 7 years old: it’s one of he first Intel i7 processors but thanks to MacOS it’s still running fluently. As I said before: I’d never buy a brand new Apple device. Too expensive and the used ones are already „idiot-proofed“. This one got a new GPU two years ago so I expect the power device and the 1TB HDD as the next parts to screw up (maybe).
But anyway, I know the iFixit videos to get my hands on that. Wish me luck!