is it possible to change the limitation of the number of layer? I work on resolutions of at least 2400 pixels and I can only add 6-7 layers. I have to get off my resolution to add more. I use PS Touch on my iPad Mini 2 Retina.
last question, is it possible to change the dpi of a picture ?
The number of available layers is pretty much resolution dependent. e.g., A 1920x1104 project lets me have about 18 layers total. A 4096x4096 project lets me have 2 layers total. (I imagine hardware plays a factor too; I'm using a Google Nexus 7 2013 running Android Lollipop 5.1. Try creating similar projects to compare.)
You cannot change DPI. Nature of the mobile beast, I guess.