in your fleet menue, you can see all stacks and how much power each one has as well as quantitiy. in all you can have as many stacks as you want but only ten stacks of ships go into battle at a time.
best advise is to know what ships you like to use and when you build them keep their pr (power rating ) as close as possible. try to use ranges ships up front and then some powerhouse ships for backup. always feel free to post questions here and good luck