I checked out the tank pictures. I like the powerhead placement in pictures #1, it appears to give the best water flow without disturbing the sand to much. By the way, it appears that you have a venturi adapter on the black power head. Is this true? If so, remove it. You don't want all these bubbles blown into a marine aquarium.
Your system is extremely young, which shows visibly. You have no coraline algae growth at all. The sand is still very immature, showing none of the visible signs that appear after copepods and amphipods begin to flourish. This is very likely because of your limited amount of rock. You really need to triple this amount of live rock for your fish to feel safe and secure, and for a nice diversity of critters to spread. Plus, you need more rock for the filtering capacity of the rock.
Here is what I would do. Go to your LFS and ask to buy a handful of the crushed live rock from the bottom of the live rock vat. It will just be useless junk to them, but will be loaded with a diversity of copepods and amphipods. Take this handful of rock(sand) and just pour it across the back glass, hidden from view by your live rock. This will help tremendously and is a technique I have used to increase the diversity of life in my tanks.
You asked about adding a Yellow Tang. Here is a post I just posted in another thread. It applies to this discussion, so I just copied it:
I know most discussions focus on the cycling process, but the cycle is actually not very important in marine aquarium keeping. We take it for granted, so to speak, but it does not really give us any information that is helpful. When I discuss an aquarium being "mature", I am looking for a few things.
1) the diatom bloom has come and gone.
2) coraline algae is beginning to cover the rocks and glass.
3) Nitrate has reached its peak and began to fall. Yes, NitrAte.
4) Your glass and sand show an abundant supply of copepods and amphipods. This becomes very visible when you clean the glass, because these little critters and wiped off into the water column, and your fish love the snack!
5) your alkalinity and calcium test results have become somewhat predictable, and your dosing routine has become standard, with little variation.
These are all signs that your system is mature and your tank is ready to successfully keep all varieties of fish, invert, and coral.
Moving on, another issue you need to give thought to is your fish selection. In my opinion, you can not keep a Yellow Tang in a 29 gallon tank. Not at all. There is another thread running titled "15g difficult". I suggest you read along with that thread as well, because the information applies directly to your tank. Yesterday I posted a very long post about fish selection. Here is the link: http://www.fishforum.com/starting-sa...fficult-30212/
Oh yes, I am 36 years old, live in the U.S. I started keeping fish at age 12, marines at age 16 or so. Also, both of those starfish you like are impossible to keep alive in captivity. They should be left in the ocean. You would have an impossible time sustaining any starfish in a 29 gallon tank. There simply is not enough life for them to graze on. You WILL kill that starfish, so don't buy it.