You can have as many as you want I believe it will just take longer to load the landscape. BTW you have a limited count of texture samplers (16) for material unless you change the sampler source in our texture sampler node 
You can have as many as you want I believe it will just take longer to load the landscape. BTW you have a limited count of texture samplers (16) for material unless you change the sampler source in our texture sampler node