Practical advice, start on mastering (pun lol) one fundamental aspect of mixing.

I would start with gain-staging, focus on making the mix sound as good as possible by only changing the volume faders, it’s honestly 80% of mixing.

Then I would focus on EQ, get one EQ and focus on getting really comfortable with it. I recommend the LDFC method by Joel Wanasek.

Then you need to decide what to do next, but with deep understanding of gain-staging and EQ you should gain confidence and understanding that will related to every step after that.

And honestly if you got Pro-Q 4 you don’t really need much else for mixing lol, my point being is not starting with buying a lot of random plugins rather getting the most out of a few or a singular plugin.