Nice work throughout. Couple of observations: one thing that concerns me is the solenoid wired on the battery especially the way you have it currently. If it were me I'd put 'boots' on each positive post AND spray with battery post spray, (before covering with the red boot(s). All other connections, black ground wires etc.; I would use liquid electrical tape, and spray the negative post and attached wires to keep corrosion from occurring.
The distance from the additional positives to the ground post of the battery has a potential to ground out when you're nowhere near the tractor- something you never want to happen.
I'd also put dielectric grease in each end of every butt splice you have at your Molex connectors, etc. to keep moisture/salt out then coat with liq electrical tape.
I say this coming from a salt water environment where I run my boat during the summer on the coast of CT. (ALL my wiring is marine grade with heat shrink butt connectors and tinned copper ring and push connectors. I like to do it once and done.
You might consider a battery box too if you have room- it keeps the weather out.
Lastly, I'd look into a 'crossover' valve for your hydraulics. One real concern with hanging a plow that far in front of a loader is lateral twist force, even more than plow blade trip force. Your plow is designed to be used on a truck frame and not on a loader, which is susceptible to racking by external forces like heavy wet snow or pushing against an obstacle that is not wanting to move the way or when you want it to.
Plows designed to be used in loader applications all have crossover valves to balance pressure exerted in ways that can/could damage the loader arms.
The plow I have has a single 2.5" piston controlled by a crossover valve and incorporates lateral float rather than vertical float used by other plow manufactures, to reduce/eliminate racking forces which can bend loader arms.
Check it out for reference to what I'm referring to: Horst welding/HLA Snowplows ~Series 2000
HLA Snow -they're made in Canada and go up to 20' wide, (with side wings)!
When you get to the 2000series snowblades click on the word 'features' to the right of the plow's pic, and it will drop down the feature list and show each part inc. the crossover valve.
I'm fairly sure you could figure out how to incorporate a crossover valve to help reduce shock and stresses on your FEL arms, for very little $.