Hi there Sivergoat 12, No your handguns do not have to be of the same calibre but it can make life a lot easier at the loading table if they are and a real lot easier if you have a reload during a stage.
I've seen pards say "Ohh I keep the .45s on this side of the belt and the 44-40s on the other, and yep there always seems ta be a mess up, ya can bet on it.
Ask around your local shoots as they'll be a friendly bunch and they will set ya straight.
Have fun .....Texas Tall.