I'm glad you asked about this before you went out a bought the clowns and anemone. First off, clowns do not need an anemone to live healthily and happily in the tank environment. Many times, clowns will not even "take to" an anemone in the tank! Since you do not have a reef system, I would not include and anemone in your tank. Invertebrates require high quality water, and intense lighting reequirements. And "high quality" for the reef system, is very different from the good quality for the "fish-only" system. While you may be able to keep an anemone in a regular fish tank setup, it will never thrive and probably won't live longer than 6 mos.
Now for the clowns. Clowns are notoriously territorial and they naturally "pair". This means, 2 is company, and 3 is a crowd. Unless you have a large tank with plenty of space and hidding places, placing more than 2 clowns in a tank will give you a fighting headache. Here's what happens. Clowns can change sexes. This means, if you add 3 male clowns to your tank, one will change into a female, and 2 will remain male. One of the males will "pair" with the female and become highly aggressive and terrritorial, making life for the "3rd-wheel" miserable. Additing 4 fish hoping that you will get 2 sets of males and females is not the answer. What you will likely get is 1 female and 3 fighting males. However, if your tank is big and you have a lot of spots where these fish can hide and stake out their territories, then give a 3-some a try. I managed, after months of fussing and fighting among my males manage to successfully keep 2 males together with the queen female
. [The female is recognizable by her size, usually double the size of the male]. Have fun!