[kazinator]

There are microcontrollers that you can program on an easy-to-use USB-based development board, that lets you debug C code with a breakpoint debugger. Your program is stored in flash memory on the chip: you can just unplug it, and plug it into your project board.

If you're going to use a microprocessor with external peripherals for everything, I'd just bite the bullet and go for a MC68000.

I have that Microprocessor Systems Design somewhere (Alan Clements), from many years ago. I remember the MC68000 examples circuits and code in it are not too bad.

Here is a possible consideration: the MC68000 has DTACK line with wait states for accommodating slower peripherals. The 6502 is synchronous: it expects peripherals to respond according to its clock, on time.