Agents Pricing & 500 Error Received in Trial Version

I want to ask that in my use case there will 100 screens it means i need 100 streams at a time of one agent so how i need to pay for and either one time or in a cycle. second question is i am using trial version for testing but getting 500 error for last 24 hours so can we relay on this api if we are planning 100 streams at a time for 8 hours continously, as well as please tell we avatar with transparent background to keep our customized background according to our need this transparent background feature is supported by the streaming api.