I think recency of experience, not hours per year, is the most important part of maintaining safe flying skills.
A flight a month is IMO the minimal acceptable amount of flying to avoid skill fade, especially for relatively low time PPL's. If the purpose of your flight is to maintain proficiency, than 30 mins of airtime consisting of a takeoff, flight to the practice area, a few minutes practicing slow flight with full flaps and recovery from slow flight, and few steep turns followed by a return to the airport for 3 circuits will exercise the essential skills.
Stalls are IMO a waste of time, as the best stall prevention is to not let the aircraft stall in the first place. Practicing slow flight and a smooth recovery from slow flight is more important. Plus all of the flight control issues are exaggerated in slow flight so if you can keep the aircraft straight and level in coordinated flight in the slow flight regime then the rest of the flight envelope is going to be easier.
I also think it is vital to do a few circuits. if you look at the accident record most light aircraft are bent in loss of control accidents during takeoff or landing.
Finally I think it is a very good idea to do a year check flight with a (good) instructor. It can be hard to self evaluate so a impartial second opinion is a good way to correct the bad habits that can inadvertently creep in.