I'm looking to buy a noise supressor to get rid of an annoying hum but reading reviews says stuff about reducing feedback. Does this mean I don't have to worry about standing too close to the amp when playing my acoustic-electric guitar. I also have an upright bass with a pickup that feedbacks when I'm too close. Will it help with that?
For the acoustic, I'd recommend this over a noise suppressor...

Feedback buster

Works well and you can buy them for under £10.
all a noise suppressor does is eliminates any sound that's coming through below a set decibel level. more often than not, feedback is a result of quiet noises and frequencies that are emitted from your amp, then picked up by your instrument, passed back through the amp, picked up by your instrument, and so on, creating the sound waves to be reamplified, and thus, feedback.

if you're using a noise suppressor, it might help, but it would also cut down on your attack and sustain, and if you plan on using it with an electric/acoustic and a stand up bass, that might be a bad thing.