Is there an actual "cheap place" for edge connectors, just now ?

However, Is the problem with the previous connectors only the size ?

Can I use those for monitor/jostick/etc. connectors ?

How can these mouses survive in such a good condition ?

Maybe they were not used in real life ...

Cheap EP128
No RF ouput, but I think this is not important function

What does "no rf signal" mean? (sorry for such stupid question...)

Regular connection with antenna cable don't work.
But also when working it is very low quality picture, for using the machine with good quality, sharp picture need a RGB Scart cable. This is why I say: the RF output not important.
Anyway I think the RF output can be repaired easy.

What about the joystick caps? Can they be obtained somewhere or one should look for a 3d printer for that?

Waiting for 3D printing...

Oh and by the way (somewhat offtopic), would it be hard to build yourself a joystick interface for old 9pin c64 joysticks?

There is the simple wiring. Not too complicated. But the autofire don't work with this solution. Need to modify the joystick, or build active joystick converter with few IC and diodes.