Automatic pH controllers and fert dosers are more intended for a larger size grow that is at the 'away' stadium. In a space you descibe as a stealth cab, your res size will be so small that even at its lowest setting you may have problems overshooting the correct pH mark without prediluting your pH down, etc. As I said, choose a fert that is already buffered at your correct range and you won't have to fidget with it so much, and don't forget t0 pre-soak your hydroton.
If you run HPS in a small space, you need an air-cooled hood. If you have some cash, look into T5 light systems as a third excellent alternative. You need to give you space size and exhaust possibilities before anyone can help you choose a lighting system. Lights and exhaust should be considered a single unit.