the best way might be to look for a fully Mac compatible mk with blue switches or, if you like more force needed, green switches from cherry or gateron first.
This way the need for (de)soldering wouldn't occur at all, for the full compatiblity others have to speak up, i only use linux and windows.
There are certain mks from time to time that would allow switchmodding without (de)soldering, but i have no idea if you would be able to open up the switches (top and bottom half) for exchanging stems and springs.
Then we've diy-kits (do it yourself) from time to time, where it would be needed to find someone, local or communitywise, for soldering service.
If this is set, the next step might be to get caps you like, but your wish of different 3D printed caps for each key would be very expensive and not even be possible for all caps.
Hope this helps to get things started.
Edit: To change keycaps no soldering needed.