Design Pattern for exposing Webservice

I want to expose an external API to my project(make an SDK in C# for the API).

What design pattern should I use so that:

1. The code for making the request and getting the response is at one place.
2. The code will make request, process the request and expose the data in Schematized from.
3. What should I do so that the code using the API can control the number of threads that will be making and processing the requests(Configuration Driven)

Please suggest some guidelines.

Thanks.