So I am using a Phantom 4 pro and GS Pro app for flying after a specific route. I was wondering what would be the best speed and gimbal pitch for video and if anyone could recommend a good altitude for landscape videography.

What I am thinking is something like this

I was wondering what would be the best speed and gimbal pitch for video and if anyone could recommend a good altitude for landscape videography
The best speed, gimbal pitch and altitude is whatever will show your subject the way you want to show it.
There's no way to specify what will be "best".