1) Agree with Plowboy, change out those valves for the ball valves, and why you are doing that, add 3 "line filters", and forget about tip screens.

2) Along with what others have said, chuck the tips, and size new ones to your specific needs, ie. gpa and speed you can travel.

3) If you want an inexpensive controller that will do a decent job, I'd look at the the Hiniker, and since your putting this behind a tractor, unless you already happen to have a radar gun on the tractor, just opt for a wheel sensor and put it on the sprayer wheel.

4) If your wanting a higher end controller, then I to will agree with a Raven. I've used Micro-teks, Dickey Johns, and even the Hiniker, and the Hiniker and the Ravens are the easiest to program and operate.