I was a CEO of group once and maintenance is always higher than you think many hidden costs. The idea of fixed costs and timed maintenance on monthly is good I also built some into the hourly and any surplus into the engine fund. Denham is a good call for a base one of the cheapest but did only accept groups up to 8. 721 mtr hard runway good fuel prices and airfield owner operated flying club on the north side so best to park north side with membership of the club. Looking at the specs this will not be a 4 seater for touring a Cherokee six would be better, the extra fuel burn is small compared to the overall costs and to keep costs down a fixed prop is much cheaper. On only 400 left the suggest TBO is 2000 hours but Lycoming expects it to only make that if operated 40 hours a month, so regard this engine as timed out for purchase. Compressions mean almost nothing it would still make full power with very low ones. On the 360 it is cam profile wear that robs power plus lots of problems with valve sticking. I would want to see at least a 1000 hours left on the engine. Don't forget a couple of mags every 5/700 hours vacuum pump the same, so at 1600 hours could lose them before TBO. Will be a very close value call. Best of luck.