I might suggest you to stick with Cowboy for sometime, since there will be newer rules for alts in CL and if you're in 2 clans, it may affect one of your clans. .
@L Which rules? You have to declare your main at the start of a season and stick with it during all the current season and remain in that clan with that account. There is also the rule where you can't play back to your former clan for 2 consecutive seasons if you play for a new clan. For example, if you play in clan A in CL9 and play for clan B in CL10, you can't play for clan A before CL12. Having accounts in multiple clans doesn't affect anything if you respect the other rules I have mentioned as far as I know.
I heard it is at each start of a new season and during all that season you declare what is your main account. What was your previous "main" doesn't matter.
I suggest you join the Cats. Do you like Lord Andrew Lloyd Webber? Do you prefer Felidae over Canidae? Do you like to go your own way? Then join the Cats.