Crowntails don't really seem to be any more or less aggressive than other tail types. I had one male who was totally hyper and one who is completely chill. Of my girl CT's, a couple seem extra feisty, but then there's the one who thinks she is a neon tetra. Mostly, it's the personality of the individual fish. For the 5G, I would second the divide and add another female. Two females without the divider would have a high likelihood of fighting.
The Boy Feesh: Indigo CT, Lavatail CT, Ghost CT, Chicory HM, Redfish VT, Magic DT
The Girl Feesh: Christmas CT, Shine VT, Snowflake CT, Stripes VT, Midnight CT, Grif VT, Tangerine VT, Wraith CT, Amethyst VT, Ice CT, Poe CT, Turquoise II CT