ya really don't make your own valves for tractor hydrualics. pressure and tolerance levels are really up there. you can buy various 3rd party kits. newer tractors you might be able to buy a 3rd function kit for the FEL (front end loader) that does not involve making brackets and like.
FEL loaders normally have either 3 levers (kinda rare these days), to a joystick with a button (button being 3rd function)
Surplus Center and look into the hydrualic listings. lots of valve options there.
most tractors you can add additional rear remotes. most tractors have some sort of factory kits for up to 3 rear remotes. you can also get 3rd party setups as well.
double check type of valve you want. some have a detent / notch to hold stuff, another might have a "float abilty", another might have some sort of screw or set piece to hold lever in wanted position. there might be a "regen function", and perhaps valves more noted for hydrualic motor vs generic hydrualic cylinders. (motor valves more likely have bigger internal passage ways. to reduce pressure of hyd oil going through the valve)
normally when you start adding rear remotes, you start looking at "stack valves" due to not a whole lot of room to place but valves and the levers, and then for some folks, they need to run some short hoses from the valve stack to another location on rear of tractor for the QD (quick disconnects).
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with your questions of front and rear.... going to push ya towards looking at a TNT (top and tilt) for 3pt hitch, basicly a hyd cylinder replaces top link and 1 of the side links of the 3 pt hitch. so you can adjust 3pt hitch from seat of tractor. vs trying to mess with turn buckles.