Get GSX Pro and FS2Crew (FS2020)

So, for years I've been using FS2020 without any addons, more than liveries, airports etc.

So, I'm thinking of lerning the PMDG 737 (and maybe the 777). Would you say these addons would help me, or will they more add realism?

What exactly is FSCrew and why are there different versions?