Logan

You are correct, they are normally pointing down. Honestly, either way can work, however with the intake pointed down the PSU fan sucks cooler air from outside the case which helps with longevity.

Are you certain that you have the USB adapter plugged in securely both on the mobo and controller? If so try plugging into a different usb 2.0 header on your motherboard if possible.

Do you possibly have the software set on "Multilayer"? This would allow you to have a different effect for each output. Also, check the connections between the RGB controller and each fan, especially the one that is acting different than the other. The RGB connections have four wires, one for Red, Green, and Blue, with the last one being for voltage. If you have a poor connection it may still work but have a color channel missing. If none of that helps try switching ports on the RGB controller and see if the problem stays on the same fan or moves to another, this would indicate if it is a problem with the controller or something else. https://www.youtube.com/watch?v=C2nzMclMLTQ

Newegg has them in the US and Canada. https://m.newegg.com/products/N82E16811999386 On both Newegg and Amazon you need to search for "c700 series", as c700p brings up nothing.

Yes it is! I'm thinking about buying a second glass panel myself, however I haven't done it yet. I did test it and they fit either side just fine.

If you are in North America, Newegg currently has them in stock. Edit: https://www.newegg.com/Product/Product.aspx?Item=N82E16811999387&cm_re=fits_cosmos_c700_series-_-11-999-387-_-Product

If possible I would use a 140 mm all around. Generally speaking, a 140 mm fan will flow more air at the same RPM, allowing quieter operation for the same cooling performance. However, 120 mm fans will work well, just not quite AS well. It depends on what kind of cooling setup you have, and how much heat your system produces; air cooling vs AIO vs custom loop, ThreadRipper or i5 etc. However, even worst case scenario having three 120's in the front and one 120 in the back will not be "Bad", it could just be a bit better.. but then it always can. My current setup is the three stock fans in the top, Noctua NF-A14 Chromax in the rear for exhaust, and three more NF-A14s in the front.