Sounds like he's made a few of the right choices already for RX-8s.
There are a few limited editions around from the various years mostly the changes were to paint and trim but pro-drive one firmed up suspension along with a few other mods, I would suggest that although it is quite desirable as a basic un-modded model the suspension would not be family suitable.
Oil reserve is much smaller than most cars as part of the desire to keep that bonnet line low in the design, this is why when oil is used it is more noticeable than other cars, so checking it regularly is a must, I think the oil usage is a little higher though, worth checking the oil and filler to check for overheating signs.
Private sellers are having a real difficulty so if you can find an enthusiast then you'd be in for a bargain time. I've noticed some dealers are selling some pre-registered ones at very keen prices so well worth a shop around them, not your area but Bristol had one up last week that surprised me (next to Lotus dealership before anyone asks).
Well finished as Stanski says, I think the dash finish is very good, Bose stereo good other one is complete pants, boot good enough to be practical and the ride is quite smooth so ok for passengers, knee room in back is cramped so if his family is long legged they will notice.