LOL at blitz with the mustache comment
looks like a playoff mustache
anyway, to blend a render the best thing to do is put it in first and make layers over it which would be your effects. don't cover your render just blend it haha
I do like a lot for a first sig, it's a lot better than my first sig. Just look at a few tutorials (I think we have some gimp ones here but I also always direct people to gimptalk.com they have tons) and I'm totally sure you'll do great.