Thanks for the enthusiast replies, it gives me a boost

I would surely setup the systems to be really easy to use, just click and play. Easy for Amiga, just start the games trough icons as normal.
For C=64 I can make a little script in basic with a "press X key for game X". I would definitely need an expansion that let me put the games on an SD card or a HD, I think there is plenty of info on the net about these kits for the C=64.(?)
Of course i'll have to check every licence that are still alive and see the conditions for commercial usage. Most of it must be abandonware tho and therefore the fees are applied to using the computer "at large".