Pretty cool idea mate. One thing I would really like to see is better Aircraft physics so that we can have a lot more RP to do with aircraft such as planes and helicopters.
I remember, like 10 years ago, when I was much younger I always played “plane crash simulator” on Roblox. Also, when I play War Thunder Planes, I always try to survive in my burning/shot up aircraft - it is a pretty thrilling experience! lol
For cruise control, I was thinking a style like Arma.
In Arma, you do Shift + Page Down. It decreases your top speed cap by 10 kmh. You can go down as far as you’d like. To put it back up you can do Shift + Page Up.
With American Truck Simulator and Euro Truck Simulator 2, cruise control works fairly nicely. With how I have my keybinds set in them, C enables/disables cruise control, - lowers the speed, + raises it and then I have some other key set to resume it if I had to stop somewhere.