Clarissa Is it best practice to download all the apps onto the owner profile, and then distribute them to each of the other profiles?
Up to you, but GrapheneOS gives you a lot of secutity and privacy compared to Pixel OS or iOS even it you stick to one profile, so both setups are great. You need to install the same app versions across profiles (you'll get an error message otherwise on the second install attempt), and I personally would just go with the owner profile as hub for installing and updating if I were you.
Clarissa By downloading the apps with known trackers into the owner profile (but not using it), do I risk having the owner profile be tracked?
Define "tracking" for yourself first (is it collecting personalized data, is it linking identifiable patterns/information etc.). But what will most likely solve your problem is denying all user apps on the owner profile network/sensor access and any other permissions. They don't need to launch or function there, just exist.
Clarissa There is a ride-sharing app called Grab that can be downloaded on one of the other profiles, but not another.
Probably the aforementioned version issue. Any app should install just fine if it's the exact same version already installed on another profile.