I’m not sure what you mean by “How much I can look UP depends on the position of the camera.” Bottom/top meaning closer to/farther from the terrain? Or something like North/South?
(I typed this next part up last night and forgot to send it so I’m sending this now as an exercise.) Okay, so for the rotation and zoom, let’s look at some example cameras for RTS’s that are pretty big names that have a zoomable camera.
There’s almost the entire “Total War” series. What they did was have the camera in the early days be un-rotateable in the X or Y axis, only Z (left/right turning only). Then later they added a small Y rotation as you zoom down, and now with their modern entries they allow you to rotate in the Y a BIT but not much- manually. If I were to guess… it’s probably kept between -90 and -30. But the modern titles also have low-poly landscape going off into the distance of each map, these angles are just to keep the camera focused on the playable landscape and not up into the sky.
Then there’s "Baldur’s gate 3. You can rotate in Z axis only, but if you zoom in, it rotates the Y axis a little more, the closer you get to the ground.
Both BG3 and the middle of the TW series have the zoom depend on math such as “Camera Z pos - ground Z pos * camera Y rot variable adjustment number = Camera Y rot” or something to that effect due to not being able to rotate Y. So the question is what would the closest camera system be that already exists to create and then branch from?