I bought 2011 Yamaha Gas Cart new 6 years ago from TV Cart Store, it had and still does, Loadstar 205/65-10 Tires and they say right on the side 35psi and that is what I keep them at. I know under-inflated golf cart tires will wear out on the edge quickly.
The Stablizer that Carts & Clubs said to add was probably this, Sta-Bil Marine Stablizer for Ethanol Gas. Since you used ethanol free gas you won't need to use that anymore. Probably didn't hurt it, since I used ethanol gas and stablizer for 4 years and have been using ethanol free gas and no stablizer the last two years. A lot of stuff has gone through my tank by now.
I have Ultimate Seats in my cart installed when I bought it from TV and they look just like this. From TV they have an 18" long support arm with rubber ends that is under the seat with velcro and you just lift it out and prop up the seat with the support. Seems Carts & Clubs should included something similar.