I have a Royal Gramma with a couple of clowns and no problems. The timing on when you introduce the fish might make a difference in a small tank, so always put aggressive fish in last. Since they are both semi aggressive (territorial), I would put them in at the same time. When I added my Royal Gramma (Ray) to an established tank, my Black Blenny (Malcom X) and he had it out for a few days (it was like watching a **** fight). Ultimately the Malcom won and kept his home sending Ray to the other side of the tank. They seem to get along fine now.
I think one of the most important things you should get is a dosing pump (multiple heads) and start on a two part of some sort (I use B-ionic because I am lazy and it works). This will really make your life easier. You can also build your own ATO with a cheap fountain pump and a float switch. Along with my DT, I have a nano tank that is basically maintenance free (or at least I neglect it) and it has SPS and softies galore that are all growing fine. If you are local (Florida), I could give you some frags to get started. I always heard that SPS are harder to keep, but I have no problems even though I don't really know what I am doing. I think the way to get into corals would be to get your ALK, NO3 and PO4 stable and then just buy any coral that is on sale and see how it does (not all corals will like your water). I used to think smaller tanks were harder to keep, but since a huge water change is only 5gal for my nano, it is much easier to care for. The key to keeping your parameters in line is not overloading with fish. As you get better and your tank matures, you can then add more fish.
I would also recommend using RODI water (either get a filter or buy from LFS) if you want any success with corals. Another good thing to do is find someone that has a great looking established tank and just copy what they are doing and be patient. Good luck!
