im assuming that the danios will be only about 1.5-2" when you get them from the store. that is the average size of them around here anyway from the store. to cycle a 140, you are gonna need quite a few. at least a dozen. you may be able to just use some feeder goldfish to make it cheaper unless you like the danios. some can look pretty good. overfeeding them can also help with cycling the tank. the uneaten food will rot producing ammonia as well. once the tank cycles, i would start adding your show fish one by one. keep track of the ammonia. once it drops back down to below .02ppm add another.