I'm planning to build a cummuter with a single-speed crankset up front and a 5-speed cluster in the back. The hub I have comes with a 5-speed, so I'm sorta working around that. It's also a mountain bike set-up.
My question is what derailleur is compatible with a 1x5 set-up? I will be using a SRAM MRX 5-speed grip shifter, but still unsure of what rear derailleur to use with a 5-speed. Looks like there aren't too many out there. Will a 6- or 7-speed derailleur work then? Or even a 9?
What about chain length for a single-speed crankset?