Sorry, don't visit CR all that often so wasn't able to get back to you right away.
In my experience with manual valves, which I had on my white GTI before I sold it, it genuinely made me hate the car for multiple reasons. I also built mine on an incredibly budget minded setup and regretted it from the beginning.
Here's what I learned:
1. Manual valves are the cheapest because they're literally the worst. They work, but they're terrible for just about everything. You have to run separate air lines from the tank to the valves, to the gauges, and to each of the bags. This means a TON of air lines throughout the car, and the more connection points you have, the better chance for leaks. Placing the valves somewhere with all the lines hanging off the back can be a HUGE PITA as well.
2. Run twin compressors before a single with larger tank. A 3gal tank will be good for a single down and up, and the twin compressors will fill it up really quick and reduce run time by a ton. A single will run forever trying to fill a 5 gal, and generally too long before it overheats and causes failed check valves, or burns up the compression ring. Not to mention, if the single compressor fails, you're beached.
3. Don't even bother with PTC fittings, and if you do, triple check with soap and water each fitting isn't leaking when they're in place. They leak incredibly easy with any bend or a bad cut in the air line. Compression fittings are the best option, IMO.
4. Even if it's the cheapest electronic management, it'll save you a million headaches over manual valves. They install 30x easier with very few wires. No extra air lines other than the ones going to bags which minimizes chance for ruptured lines or leaks. Most have PSI presets so you don't have to fuck with the manual paddles for 15 minutes before you drive to get the ride height right. Also, I would much much much rather replace a bad or stuck valve than chase down 40-50ft of air lines looking for where a damn leak is coming from. The chance of them failing isn't really all that often and if you prep the system with anti-freeze in the winter, you'll never have freezing. Freezing will happen with any system without proper winter prep.
TL;DR - Do it right the first time, otherwise you'll hate life.