To test out FreeNAS, you do not need to build a system. Just download a free VM solution such as VMWare Player and install it. Now you can create a virtual FreeNAS system. Keep it basic and simple, a single virtual hard drive for booting (4GB thin provisioned) and a single data drive (200GB thin provisioned) should be fine. Once it's up and running you can try some backup solutions. You only need a few files, should be easy to do.
The link you provided looked pretty good to me. The instructions were clear enough for me to follow if I were to use them.