This week I saw a couple of blog posts with projects relevant to this sub-forum. As we've said, there are many possible approaches to getting started, and these people have of course picked one - it's worth understanding what they are trying to do and why, before choosing your own path.
Having posted about two, another showed up, and I'm going to add a fourth. There are also several mature from-scratch projects which have been mentioned previously - I'm not going to link those here because it's extra research, but they are just as worthy of a bit of study. Perhaps others can help provide good links: preferably to development stories rather than finished projects.
3-Chip computer by Stian Søreng (of 6502asm.com fame) uses an ATmega and dual-port RAM to address the bootstrapping and I/O problem. The ATMega drives a display by snooping the RAM, so the 6502 acts as if it had memory-mapped video.
The Übersquirrel by Scot Stevenson is at the free-running tied-off NOPs stage. He uses an Arduino to snoop some of the address bus so he can see what's going on.
The MOUSE project by Mario Keller (in German,
auto-translate here) uses a RIOT and an EPROM. He used his Ardiuno-based
MEEPROGRAMMER project to program the EPROM.
Finally, the
Veronica project by Quinn Dunki is a must-mention because the write-ups are so good: covering successes, failures, and debugging travails. This grows into a multi board system with video out, but the first post covers free-running and
the second post covers manually programming data into RAM using switches and LEDs.