Electical Engineering accepts design reviews under some conditions, and CPU design
and instruction set matters are on-topic there.
However, you must take care that the question is not too broad, but this is probably the case for all sites on which it would be on-topic. So, try to narrow the question down as much as possible, and focus on the choices you're not sure about. You could even break this in multiple questions, one for each specific concern you have on your design.
You can't post your entire specs and just ask "what do you think about all this?".