Your biggest clownfish is going to be your female with the next in size the male. Other clowns in the tank are juveniles which are no sex. If the female would die the male would take the place of her. The actual change takes about a month to complete. Once a female is a female she cannot change...
Also make sure you have the proper lighting and current depending on what type of anemone you may choose. :)
Bubble-tips are usually the easiest to keep, IMO.
Damsel fish are aggressive and will clash with smaller fish and most definitely your clownfish. Also what kind of lights are you running? Anemones can get quite picky about lights, also clowns do not need anemones like most people think. Anemones in the wild are used for safety and defense, in a...
I like Chevrons but as you mentioned there is a chance for aggression from the other tang. Have you thought about a Bengaii cardinal or a fairy wrasse? Very colorful and they will not spark aggression in the tank.