Are you hearing electronic noise or ambient noise? Unless I record at a ridiculously low level, my ambient noise level is far higher than any preamp/mic noise, even using dynamic mics like my SM57 or my Senn e935. I'm going into a Tascam 16x08 which is probably similar in spec level to your 18i8. I don't even have a Cloudlifter/FETHead. I've done vocals with the e935 just plugged into the Tascam and it was perfectly usable singing around 4-5 inches away.
Not seeing a big waveform on the screen doesn't mean that you don't have 70 or 80dB of Signal to System Noise. Most of the times, if I normalize a signal so that I can see the actual waveform in Reaper without using the zoom function, it's only 15-20dB. It's handy to see the waveform if you're editing so that you can cut and paste with a bit more precision, but that's the main reason I do it, unless I get a track that is unusually low, and I have trouble getting enough gain with the volume maxed out compared to other tracks.
In any case, doing a normalization should not affect the sound at all. Remember the saying that a rising tide raises all boats. The differential of loud to soft is still the same.
If you are concerned about the base noise level, then do a recording with the mic set up with the "low" waveform, then be quiet and see what the actual noise floor is (really easy to see with something like the Blue Cat Analyzer). In many cases, you're looking at something -50 to -60dB in most rooms.