4 doors, fun, and sub-£5k? RX8 all day long.
There’s plenty of internet folklore and urban legend about them, but 90% is regurgitated hearsay from folk who heard a guy down the pub who once read a Jeremy Clarkson hit piece on the Wankel engine and have no actual experience of them.
They use oil, yes, but it’s bog-standard mineral oil at ~£3/litre for every couple of thousand miles so I can’t see what the fuss is about.
They use petrol, yes, but if it’s a second car primarily for fun then shouldn’t be a major consideration. 25mpg is doable.
The 13B-MSP is a different beast when it comes to engines and accounts for pretty much all the horror stories you hear about the RX8. They’re nowhere near as bad as they’re made out to be though. They need a more involved maintenance/service regime, and there are various “upgrades” that come highly recommended (engine bay heat dissipation and changing plastic components in the cooling system for metal being the main ones) but for all but the most incompetent of mechanics it’s maybe half an hour every month at most.
If you’re concerned about engine life get a “broken” one for around £1k and spend £3-4k on an absolutely top-notch rebuild, and then have many years of worry-free warrantied driving enjoyment.
Or you could chicken out and get a Golf GTI.