I keep a pulse oximeter handy on all flights and check it occasionally in case you get a carbon monoxide leak. When I was younger 12k was doable. As a young aircraft crew member I did go to the high altitude chamber was an enlightened experience.
Look for a 150 that’s been upgraded,what looks like a good buy can turn into a real money pit when you start dealing with avionics. I have a 150 l model and it’s going to be my last airplane.
Back in the day grass operations were part of the training. When I rented the flight school owner would approve grass operations on a pilot to pilot basis.
Returned a rental back at the airport,they didn’t come to pick it up for two days which they tried to charge me for. Also a reservation is not a guarantee of a car being available.