I don't recommend adding a red star to a new tank, and ideally they should be added to larger tanks. Wait about a year or so until the tank is well established and then consider it.
As for bioload, inverts don't add much bioload compared to a fish. However, you are planning 4 fish in a 20 gal tank, which is way overstocking the tank.
By the time you add enough live rock, and optionally live sand, that 20 gal tank is only holding about 15 gal of water. You want to stock a tank at the rate of 1 inch of fish per 5 gal of water. This works out to 2 or 3 very small fish or 1 or 2 larger ones. You also need room for growth.
Yes, you do see people often go over what I recommend, and sometimes they get away with it, but it's a very difficult balancing act. In this case, what would be a minor issue becomes a disaster often resulting in a tank of very dead livestock.