Try this exercise a couple of times: Start by not putting anything on anything, and not assuming that you have to put anything on anything. Then make a challenge out of just how good you can get things to sound with zero plug-ins.
When, and only when, you're absolutely convinced that you've taken the mix as far as you can and done everything you can to make your mix sound good, then listen to what you have and decide if and where you'd still like to make improvements that can absolutely only be done with plugs and where they are needed.
Ideally, the amount of them you need to throw at the stereo mixdown should be minimal. Make the mix sound good before you master, and don't use mastering to do what should have been finished in the mix.
G.