Nodes are free. Just download NIS and run it. And you are running a full NEM node, the same way you could be running an Ethereum node by executing Parity in your computer.

In order to harvest you must own more than 10000 XEM. Owning less than that amount will never allow you to start harvesting, as you will never get to 10000 vested XEM in your balance.

To harvest you just have to activate your node harvesting feature. Many people do it by remote harvesting. But some prefer to do it on their own local machine.