Awesome thank you all!

Whether you have a SiteRubix or your own domain, you will still get support. You can keep your siterubix and use it for testing things that you may want to do on your website. Of course there is nothing better than getting your own domain as soon as you can so that you can already started building your business while learning.

Hi Tommy
I say definitely get your own domain name, and a .com if possible -
... like Craig said, you can host it right here at WA.

I did it shortly after joining here - in my opinion, the sooner the better

So I can create my first page in SiteRubix... move it to my own domain... and still have it supported by WA?

I would go with your own domain. I feel it looks better. You will still get the same support assuming you keep your site hosted at WA.

Your own site will have some better ranking power by virtue of the fact that it is a top level domain.
There is no rush but it can help to have your own domain.