Since the clowns will be the first fish in this tank, go slow. With every fish you add, you'll have to monitor and stabilize the parameters.
On top of that, the addition of brighter lighting, may throw things off and lead to more algae which you'll want to get a handle on before you and an anemone.
Since I believe you said you already have the clowns on order, I guess you have to get them now and get them used to your tank while you are looking for the BTA (Bubble Tip Anemone). A RBTA is a Red Bubble Tip Anemone. The color of a healthy RBTA is usually dark orange. There are GBTA (Green Bubble Tip Anemone) also. However, I usually don't here of them splitting as often. The RBTA and the GBTA are the same species Entacmaea quadricolor.
If the clowns are not on order, I'd get the BTA first and have it settle down into the tank and the position it prefers. When you get an anemone remember to cover the intakes of your powerheads with foam. As the anemone will wander around the tank looking for a suitable spot to call home.
Then, when you add the clowns, the tank would already have an anemone and they will hopefully check it out and host in it really fast.
The first time I added an anemone, I already had clowns for awhile and they were used to the tank and where to sleep, etc. It took about a year before they decided to switch and host in an anemone.
Before you buy all these critters, I would encourage you to read this
http://reefcentral.com/forums/showthread.php?threadid=298642
and do some research on the anemone and clownfish forum
http://reefcentral.com/forums/forumdisplay.php?forumid=36
Hope that answers you questions.
Best of luck,
Roy