Most turtles cannot be kept with fish as some have different temperature requirements or they will eat your fish. You might be able to create a paludarium with smaller, non-aquatic turtles, like box turtles.
It depends on the size of the aquarium and the adult size of the fish. Let's say I have 9 one inch adult tetras. I could add 9 tetras to a 10 gallon tank. However, let's say I have 9 ryukin goldfish. I would need a 300 gallon tank for the 9 ryukin goldfish. What size is your tank and what do you have in mind? Also, you will need to cycle your tank before adding any fish. You will need to buy a liquid test kit for ammonia, nitrate and nitrite.
I don't know much about Fengshui as it deals with fish, but you could purchase a 10 gallon tank or larger and keep 9 neon tetras and still comply with the Fengshui rules.
Try aqadvisor.com/ for stocking suggestions.