Steve, welcome to WFM! The best Deere garden tractor site anywhere!
My parents bought their 320 new in '92 and it's been a great tractor for approximately 1600 hours and counting. Keep in mind that the Kawasaki engine has a plastic camshaft gear that is famous for breaking. The 320 is very similar to the 285 Fuel Injected model but with hydraulic lift. Other tractors in the same family are the 240 and 260. All the implements are interchangable (mower, blade, tiller etc.) As far as I know. I believe Terry has just posted a thread showing the attachments availability/interchangability for various families of tractors in another thread. You need to consult the Late model thread for the 320.
Brent