Greetings Mike. Sorry to hear that your situation requires you to make such a choice. I know that working as a photographer can make demands about whast equipment you choose that don't neccesarily jibe with your desires. But reading your post above about the M8 makes me think it's the right choice to sell it. Others who have suggested you sell it have made valid points about it's value, but the greatest reason to sell it seems to be in your two posts. If it doesn't satisfy either your heart or your work as a photographer, it should go.
As for your other cameras, I'm with you- I'd keep the M3 and the M7. The M3 perhaps is my favorite 35mm film camera- I would not be without one. Because of it's history as the first M, it's wonderful finder, and the unbeatable build quality, it's certainly a keeper. The M7 seems to me to be a great compliment, adding sensible features and great functionality. The fact that these two seem to have such a nice balance in technology and timeline is also appealing. You could do a lot worse. Selling the M6 and the M8 should be no trick. Your bank account will be healthier, and your cabinets and camera bags less crowded- both good feelings.