Just going off of my own experiences with clowns -- mated pairs are very aggressive. IMO/E, 3 or 4 pairs would only work in the short term, and would be a disaster in a year or 2 when a mate pair forms.
+1
The clowns (from my experience) will not live in peace with other fish in "their" territory. The addition of an anemone just imcreases their nasty behavior (or did mine anyway) Also, some anemones are VERY difficult to care for and should be avoided. Because this is your first tank I suggest going with BTA/RBTA nems.

They are beautiful and much easier to keep (and more forgiving) than other anemones (I'm sure others can chime in and give a few suggestions). Another plus to keeping these is that you can have them brushing each other and they wont kill each other (mine don't anyway) so you don't have to worry about dying anemones due to chemicle wars.
Clownfish I'd highly suggest avoiding if you are hoping to keep more than one pair are maroon clowns. These are massive, vicious clowns and will put you at the highest risk of having aggression issues.
Back to the anemones. Treat these like a coral: High (reef capable lighting) and fabulous water quality are the main two. I'd wait a mimimum of 6 months before adding any anemones as that will give the tank a little while to mature and you time to get a hang of things

I also want to point out that it is not a sure thing that the clowns will take up the anemones as a host (really a 50/50 toss up) but either way they are both beautiful animals.
To finish up my thoughts on anemones I want to say that pumps are not as big a problem as they're made up to be. I probably have the most "anemone-death-trap" pumps out there (I have 3 of them and 2 RBTAs which have been in the tank about a year

), my nems moved all over my tank for the first 2 months I had them, and they haven't been chopped to bits (knock on wood)
I am upgrading and putting vortechs on my tank in the next few days so I can let you know if that changes things up (in the nems behavior and what not) but don't sweat the pumps as much as the care of the nems themselves because you really do want a nice amount of flow on your tank to keep many species of fish (and the anemones)
One more thing...lol
Because of the tank being mostly anemones and clownfish I'd only go with a couple other, bigger fish. I'd avoid anything that likes to hide in little cubby holes in the rock because they'll have a greater chance of getting stung, if not eaten, by the nem.
What other fish are you looking into?
I wish you the best on your build and keep as updated!
