There’s never going to a single answer to this question. You have to determine what works best for you and your team.
As a good start I setup my GIT project with the following - A new, community-hosted Unreal Engine Wiki - Announcements - Unreal Engine Forums. It gives you a list of what you can safely ignore from source control.
Check out Example Project Content Structure (GitHub - Allar/ue5-style-guide: An attempt to make Unreal Engine 4 projects more consistent) Actually, the whole article is a good start for you.
In the UE4 editor I set my folders to blue for assets that I’ve created and want to add to source control and everything else is grey and could be downloaded from the marketplace. This works for me.