What would I buy if I had it to do "over" again? An M20E. It is what I could afford. Four seats full tanks can't be done in an F or a J with "big adults". They are all 3 seat planes UNLESS you are going on a 1-2 hour flight. I did those flights with teenagers (son 5'10). Room in back is fine unless your legs are in the top 10%. The F model is nice because of the added baggage and fold down seats. That's it. The E is a little faster than the F and C.
I don't think $40k is a good buy-in price point for any of the three (C,E.F) as you WILL be spending a LOT of money on fixing and upgrades. ALWAYS cheaper to buy a plane that someone else has upgraded and taken care of...FLOWN.
Fuel tanks, Engine/airframe corrosion, and old avionics are the BIG dollar gotcha's in vintage Mooney's.
Find a Co-Owner and get the F OR J that will make you and your family happy for a long time. For $80 grand you can get into an airframe that should not (but might) nickel and dime you for maintenance and WILL have equipment you will want to upgrade.
Good luck. Have fun. It is a BUYERS MARKET.