If you do VERY RELIGIOUS water changes and keep an all seeing eye on your water params, yeah you could get another. I personally would stick with just three fish. 30 gallon tank right?
You are on the right track. GRab som e more LR and wait as long as possible before adding any fish. The longer you wait the more bio filtration (copepods and other beneficial bacteria) will build up in your tank causing a better stability. In a few weeks, when the water is done cycling get a clean up crew to maintain unwanted algae and such, then afew weeks later add your first fish. If you get a clown, you may want to add it last as they can bedcome VERY terrritorial. The gramma should probably be added first as they are VERY shy and will need time to feel comfortable in its new home. Keep the pics comin.