I am working with AndEngine and OpenGL ES 2.0. I keep reading about GL_MAX_TEXTURE_SIZE and how I should keep my texures under 1024x1024. I started
If you still have the individual image files, breaking them into small sized Atlases or custom sized atlases is easy if you use the TexturePacker2 tool from the LibGdx library.
I don't know the exact limitation of devices, but it's always better to take into consideration the lowest end of device you want to support and build upward from there. Using the LibGdx tool, you can easily change your mind later, so it's the most flexible solution.
Look at: LibGdx TexturePacker