I found that the P4 captures the northern light quite beautifully on standard camera settings (just go as high as you dare

but there are probably some experts here that can give you some pointers that I can´t. Regarding active track vs follow me mode, i have for the most part been using the Litchi app witch litchi leash, and found it to be working quite well. I´m not sure how familiar you are with the 3rd app Litchi, but here is a video on the litchi leash anyway :
In DJI app, my experience is that the active track still needs some work as it tends to lose its way quite easy. Follow me mode works better, but then you will need the controller with you. With Litchi, you only need your phone in the pocket. There is a lot of information and youtube videos online, witch can give you better information then i can, so have a look

Good luck, and post back to me if you encounter any problems and i will try to help as best i can.