What hfs and Dgiant said.
Also what Keef said, with a proviso about the oil. Oil should be checked every other petrol fill up and
may need topped up. Oil consumption will happen but varies according to how it's driven. If you rev it up to the 9400 red line constantly, you'll need to top up the oil every other fill up. If you just rev it all the way up once or twice per trip, then you won't need to top it up as often.
It is a great car, if you get a good one. They are cheap to buy, but watch out for the extras like petrol, oil and tax. Budget for about 21mpg average and, if you can cope with that, go for it.
There's not much difference between the 192bhp and the 231bhp but the 231 is slightly quicker, as you would expect, but there isn't much of a difference in fuel consumption. Trim levels are pretty much identical and the only major differences are that the 231bhp one has 6 speed gearbox, higher rev limit, headlamp washers and Xenon headlamps.
Your journey is a bit short. It will have warmed up in that time so there's no worries about flooding it. It may not like it long term though as it does need to be revved at least once per trip and, if you can't rev it up to the beep on the way to work, you should take it out at the evenings/weekends and give it a thrash to keep it functioning properly. Once warmed up, it's practically a necessity to rev it to the 9400 red line regularly.
If you decide to go and look for one, the thing you must do is to drive it, or get the owner to drive it, until warm. Stop it and leave it for 2-3 minutes, then try to start it again. If it doesn't, or if it struggles to start, walk away. That's the first indictaion that the engine is on it's way out. If it starts the same as it did when cold, then that's a sign of a good engine.
You could join the
RX8 owner's club forums, but you do get a fair few horror stories there, so don't believe that every RX8 is a unreliable money pit. I've had mine a year, done 11,000 miles and the engine didn't need anything done other than an oil and filter change at it's last service. If the rotary does go, £2500-£3000 will get a you a good, guaranteed and warranteed, rebuild. Bit expensive, but not the end of the world.
So to sum up. A properly looked after RX8 is no more unreliable than any other sports car. It may not be ideal for you as your commute is a bit short, but get it out on the open road and it's a great handling, fun car.
Just ask if you want any other info.