I know so many people who think they can just shortcut the mix and slam the compression from the start. I'll say this again and again and again: Make a mix FIRST before you put any limiting/compression on the stereo mix. What happens when you leave it on from the beginning is you raise the vocals and the vocals become what limits the mix, so then you raise the kick drum because you can't hear it anymore, so then you raise the guitars because now they're too thin, so now you start over and back off on the kick, but now everything else changes drastically when you do that.
That's just a start.
From there, you don't need much of a slamming compression afterward... just a L1 or L2 Ultramaximizer with maybe a -2 to -4 dB threshold.
Some people are stuck on always using between -4 and even -8 to -10 dB threshold in those L2's. I've used -6 dB as my most drastic, but never higher than that.
Too loud is when things start to sound "grainy" and "congested" when you're using too much compression. Too loud is when it just clips and pops and crackles because you go over zero (or +6 if you're still analog, but who is?) Too loud is when the radio is quiet compared to your mix.