i am not a mastering engineer and shy away from the process for anything i work on. i usually send my clients to a dear friend, Nick Dragoni, at M Works in Boston, who is fabulous, or Dan Countant who is Sun Room Audio (J Robbins recommended me to him when we produced a record together), or Joe Lambert Mastering. all top notch people.
as for mixing, i do that for a living and can speak great depths about it!
more then having a quiet space or “proper space”, have a space or two you know SUPER well. like, hey, this Pink Floyd track always has crazy bass when i play it on this system. etc. checking mixes there against your own can be the most useful.
there is a great plug in called Magic AB. you throw it on your master bus and load in a bunch of audio tracks from other releases and you can very quickly switch between your own mix and others. you can also level balance too. remember, our ears naturally amplify lower and higher frequencies as the sound gets louder.
i have NO idea what “normalizing” entails and i highly suggest to stay away from it.
one other thing to consider is when we record on tape, the medium naturally rounds off peaky transients. when we mix down the line, these spikes will start to trigger our bus compressors/limiters at a lower level. lots of peak limiting will go a long way at making a file that can be mastered louder (note: the mastering part should be where you focus most on loud, not the mixing. i usually send files to mastering engineers at -10db or more.)