A GFO (phosphate remover) might be a good idea, but I see no need for a nitrate sponge. If I were you I would remove the regular sponge in the AC unless you are replacing it weekly as it will become a "nitrate factory" all in its own accord.
In the end though, keep it simple. You will be well rewarded.
I kept a 33g LPS dominated tank quite successfully for 2 years with a very simple setup. Didn't even have a skimmer on it. You can find pics and details on here if you search for "Myka's 33g".