It's unclear what you're asking for here? The Raspberry Pi Pico and Raspberry Pi Zero are existing and very well documented ARM based single board computers.
A search of the interned didn't turn up what I was looking for, but I'm very new at hardware work. Perhaps newer chips have such tight timing requirements that you can't work with them without using a SOC?
If you're just looking to breadboard up a computer but don't want to go back to 8-bit processors, the Motorola MC68000 / MC68008 used in the original Apple Macintosh is a 32-bit processor in a DIP package running at a manageably low frequency and can be found on eBay inexpensively.
No. The busses used to access peripherals and memory are not suitable for off-die use. (This goes for all ARM cores, not just Cortex-M0.)