In version 4.6 and up using DirectX 11 you can use up to 128 samplers by changing the sampler to a “Shared Sampler”. Click on the texture sample and then choose from the details panel either “Wrap” or “Clamp”. It is usually Wrap but to double check open the texture to see which format it uses.
Otherwise you are limited to 16 samplers, with some being used by the rendering engine by default. I have an ocean material that uses 10 of the default 16 without any textures present, it depends on the type of material (translucent, opaque, TLM_Surface etc.). If you are creating a mobile material it is even lower, just 6.