Clark Do you think it's better to install GPS in a secondary profile (along with all the apps that need it; in my case, banking/identification apps), or do you think it's better to simply install GPS in the Owner profile?
Depends. Would you like to be able to distribute apps easily into secondary profiles? The owner profile has the unique ability to do so. If you have any apps from Google Play that can operate without Google services, then you may wish to use the Install Available Apps feature to separate Google Play from those apps.
How much battery does it drain, using it on a secondary profile?
I have Google Play running on Owner and a Secondary profile, and still get 1-2 days of battery with moderate, non-intensive use.
if one was to install GPS in the Owner profile, how would you make it so that the app had the most minimal permissions possible to still be able to work?
The only permission needed is the Network (for all 3 components I believe?). The only other thing to consider is the battery optimisation exception if you want notifications, as described here:
You should give a battery optimization exception to Google Play services for features like push notifications to work properly in the background. It isn't needed for the other 2 apps.