Thanks for your question!
Unfortunately, I personally do not know any other video storage sites that can store .mp4 files other than the ones we suggest on the Video Player Symbol documentation.
To answer the second part of your question -
Most devices have an in built accelerometer to measure the tilting motion and orientation. We can utilise this information and change the experience according, using the accelerometer node that can be found in the hierarchy of every Studio project.
The accelerometer node has 4 properties: landscape, portrait, landscape inverted, portrait inverted. Each of these properties can be set to a different state, making the assets in the scene rotate and move in depending on the orientation of the device itself and the state that is assigned.
We have a great video on UI: Orientation which explains this step-by-step, so be sure to give this a watch! The tutorial only shows rotation of the UI assets, but using the same process, assets can be resized and scaled.
Hope this helps and please let me know if you have any issues.
Look forward to seeing what you can create!