[lcstorc]

Welcome to RS!
I wouldn't stack the rock against the back. You want to leave room for the water to circulate.
You got lucky on the heater believe it or not. When I did a very similar thing the heater shattered when I put it back in the water. Maybe you were smart enough to unplug yours. I wasn't and it was a mess.

To start your cycle go ahead and add a piece of raw shrimp from the grocery store. This will provide the amonia you need to start your cycle without risking the life of a fish. Then test test and test some more until you have no amonia and no nitrite. Then it is time to start water changes.
Also I would hold off on the purple up until you start adding corals and even then I don't use it. It is primarily calcium which you don't need right now since you have no corals to support. Your salt mix will give you plenty for corraline etc. Also purple up can throw off the chemistry in your tank by raising the alk as well as the calc and leaving the tank unbalanced.
Read up on the chemistry threads and it will make more sense.
Enjoy.