No matter what you do, you will need a flowmeter and servo valve. TeeJet makes those, as does Raven. How many sections on your sprayer booms? Solenoid valves wouldn't be my first choice and I'd look to replace them with something like a TeeJet 440 Series manifold when you get tired of fooling with the solenoid valves. As for the console; you almost there already with your 500. Used EZ-Booms for around a $1,000 are very available. Simply plug it in to the 500 system, hook up the flowmeter, servo, and boom valves and you have on-screen coverage mapping, rate control, & sectional boom control.