I have more then 3 PGs, I like to play like this. I imagine most people prefer to stick to their 3 and just level them but I like to think I'm not the only one. The only problem I encountered till now for having three teams is with inventory, and with just 2 button it would become much easier. -Make items available: like in X-COM a button that remove all items from PGs not in the active party. We already have a very good Store/Retrieve system to manage the other teams, no need to have duplicate items sitting around unused. -Order by last acquired: so you level up a team for a while and go back to another one (via store/retrieve). In a quick glance you can easily see which new fantastic items you have looted with other teams
One tip is to create BLANK/CLEAR save in your Keep with naked & removed characters and use it to reset items when building a new party.
