I think you'd find that once you dig into those old machines it's a lot simpler than you think. The 6502 for example is pretty easy to interface. Electronics knowledge isn't much needed at first, as it's mostly just logic. You can make a simple "computer" on a breadboard that just cycles a no-op through all of memory: https://coronax.wordpress.com/2012/11/11/running-in-circles/
From there it's not a tall order to start interfacing SRAMs and some EPROMs and a UART chip and you can get a machine you can connect to over serial.
The Z80 has RAM-refresh support built-in, and can be hand-clocked if you wish making it one of the simplest processors to run - in terms of required external components.
From there it's not a tall order to start interfacing SRAMs and some EPROMs and a UART chip and you can get a machine you can connect to over serial.
Just try! It's worth it!