Nobody can tell you have many channels you need. What do you want to do? If all you're recording is a synth with one output, then all you need is one channel. I don't think anyone records (solo) vocals in stereo. Most instruments are mono too, except synths. Unless you're really trying to capture the space you're in, in which case you probably want stereo - but unless you're recording in a church or concert hall, you aren't. Quite the opposite, actually.
I don't worry about sample rates myself. But really, just trust yourself. Record something and listen to it. Are you happy with it? Don't lean on what people on the internet say.