A carpet anemone will grow too large for that tank, it most likely end in death. The two tangs will also die in a tank that small. I would suggest a 100 gallon aquarium minimum for housing tangs, they need alot of room to swim or they get stressed. Two clowns may or may not be ok for a tank that size. Maroons would not be a good choice but Perculas or Occelaris should be ok. Why do you want to use old tank water? If you are trying to bypass the beginning cycle you should use fresh clean ro/di water with cured live rock and sand. Most of the bacteria is not in the water but actually in the rock and sandbed. Get a bag of sand and some dry or live rock, then aquascape how you want. Take a few cups of sand from an established tank and mix it in with the bagged sand. You may or may not get a cycle, if you do it will be a small one. After your cycle is complete should you get one, you can add in a small CUC. Shortly after you can begin to add in fish if your water tests are good.
