In reply to TiagoBrancoEmidio:
Hi. Although you seem to be getting good advice on this thread (so far), I would caution you against relying exclusively on information you get from an online forum. Having said that ....
There is a principle in climbing known as redundancy which is important to understand. In the context of setting up a bottom rope (aka top rope), this means using multiple anchors (usually just two but bombproof ones) and arranging the rigging rope so that if one anchor fails the other will still do its job. This normally means tying a small fig 8 loop in your "V hang" at the pulley point. You don't need multiple loops or multiple crabs, but you should always use a locking crab (or two snapgates/quickdraws with opposing gates).
As others have said, the back-and-forth sawing action of a dynamic rigging rope as it stretches will wear it out very quickly. Get yourself some static (strictly speaking, semi-static) rigging rope (15 metres is common for this application), and a couple of rope protectors (or improvised padding) so that your rope has a chance of lasting a nice, long time.
I would advise getting an instructor or a trustworthy, experienced climber to show you this set up, and point out the common pitfalls; or, at the very least, consult a good instruction book (e.g. Libby Peter's books).
Hope this helps