The best OS to use

First thing you need while setting up an Outsourcing infrastructure is an Operating System. And it is better to go with the Open Source breed. CentOS is a good distro with ample support, large and helping community and good hardware compatibility.
CentOS is a community-supported, free and open source operating system based on Red Hat Enterprise Linux. It exists to provide a free enterprise class computing platform and strives to maintain 100% binary compatibility with its upstream distribution. CentOS stands for Community ENTerprise Operating System.