I have a 1971 PA-39. Your left engine and prop are the easy part; the right engine is the one that goes the other way. Issues:
– When you first fly a “normal” plane, you will quickly remember that you have to use right rudder on takeoff
– Seriously, my main operational issues were the two times I was stopped in my tracks when the right starter (original Bendix drive type) decided to call it quits. Opposite direction Lycoming starters aren’t lying around at every airport, unlike the normal ones. I finally got a B&C starter (Sky-Tec is good too – I have one on the left) that has worked fine since (had the plane 20 years/2000+ hours now).
– Nothing else has been a problem. If a generator or vacuum pump quits, you have another to fly home with anyway, and I’ve never had a governor quit.
– Availability of the counterrotating parts is no problem (except for local FBO stocks – see above) and pricing is not particularly different.
– Not related to it’s being a C/R, but even more safety: I put VG’s on it several years ago. No noticeable difference in anything except when I played around with single engine stalls (“dead” engine power at 10-11″ MP) and ~70% on the good engine. No problem controlling wing drop with rudder and aileron, even when provoked into the stall – amazing and nice to know if things go south right after takeoff (OK, 100% power is different, but I was impressed).
Enjoy your new flying machine!