The clutch isnt a on / off switch so you need a lot more subtlety in working out when the noise comes and goes to work out what is going on.
With the clutch up in neutral, touch it with your foot and listen, press it very slowly down listening all the time and feeling any change with your foot. When does the noise go and when does it return? Same goes for letting it back up.
With these gearboxes there's a high chance it is more than the release bearing, but you might be lucky.
For a lack of power you need a code reader to see if any faults are logged and more than likely a compression test before chucking money at it.