Can I use assets purchased from Fab.com under the Standard (Personal) license to develop games with Unreal Engine and then use them commercially?
Short answer: yes.
As far as I know, both personal and professional tiers of the standard license allow commercial use of the resulting game/film/final product. The only thing you’re not allowed is to resell the assets you have bought under any tier of the standard license.
What about free assets? Can I use them right away?
Yes you can.
However creating github or gitlab (or any other version control repository), and making it public, is sharing assets. And its grey area. For eg creating indie team and collaborating on some project, where not everybody has his/her own copy of assets. You are technically sharing assets outside of your game. So for that reason for eg. i cannot share my github projects that are in portfolio, only pictures/movies.