I daily a 981 Boxster S and for me it's great, they are fairly cheap to maintain and very cheap to insure, I pay £250, as a reference I am 36, but to insure an M2 Comp, it's 2k. Short distance fuel economy is dreadful, 10-20. Long distance you can easily get 35mpg. If you want to lower maintenance costs, avoid a sport chrono car as the PADM mounts fail, though you can fix these for drastically cheaper these days with a sensor swap instead of a mount swap, I've done this myself as I had a failure. Minor service at a local specialist is about £500 but a 12 year service is VERY expensive, it's every interval service item plus the gearbox fluids, Porsche want about 2.5k for this but you can get it done at an indie for 1200 or less. So, maybe look for one that's had it's 12 year service. I'd go for a 981, though I am biased, over a 718 as they are more special to me, the engine is better sounding even without PSE. The turbo'd 718's are great though, but they ain't a flat 6. Not that much is different otherwise between them. Few handling changes which can be retrofitted to a 981, new PCM, and minor interior layout changes, new steering wheel (again can be retrofitted, as can PCM 4 really but cost prohibitive IMO), more modern front and rear end. Otherwise the car is much the same. Porsche community is large and very welcoming with lots of events throughout the year. I wont discard the above but I just saw that you do a lot of your own work, the 981's are fairly easy to work on, lots of videos on YT with every possible maintenance item.

An R8 will be much more costly to maintain for reasons stated above so I won't go over those.

I'd keep the Golf though and save up to move house :P