If you mean I'm the person who told you to do that, keep in mind that I don't have any idea whether the problem I was hearing was caused by the samples themselves, it could also be the resampler or your mixing settings causing it, in which case EQing the samples wouldn't help. I was just pointing it out so that you could figure out what was causing it, and potentially fix it at the sample level if that's where it originated from.
As far as noise reduction is concerned, if you have a very bad case of a noisy recording (e.g. because you're using a low quality mic which is noisy on its own, not just because your decent mic into decent preamp is picking up some of your computer's hum from a few meters away), even the noise reduction tool in Audacity can be better than nothing, but it's important to find a balance where you're getting rid of some of the noise while keeping the actual signal mostly intact, instead of trying to get rid of the noise completely and destroying the actual signal in the process. In my experience, having a low sensitivity and 0 frequency smoothing is going to get you the best results, and the residue option is useful when previewing because it lets you listen to what you're removing from the sound (so if you only hear noise and no signal using residue, that means it's safe to switch back to reduce and render that setting).
However, I don't think you necessarily need to do that. If there is noise in the samples, it's definitely not loud enough to be audible in the full mix.
EQing in Audacity is suffering materialized. Instead of Audacity (an audio editor), you're going to need a digital audio workstation, because DAWs are capable of realtime processing which is pretty necessary if you actually want to hear what you're doing. FL Studio was recommended above and I'm also an FL user, but it's definitely not the only option for a DAW and some DAWs (e.g. Tracktion 7 and Cakewalk) are even legally available for free.