With those parameters a Wag-Aero 2+2 (I'm almost finished with my Wagabond/Vagabond project, so some bias here)would be a fine choice, plenty have been built and plenty of Piper parts around that you could work into the project. Warning though you'll probably have 40k in it at least when it's done. You can buy a fairly cheap high wing four seater, and build something more unique and smaller for "sport" flying ect. Good Luck!