Let me add my welcome to you, too. I assumed when you wrote "in check" that you feel that you don't want things to run out of control and end up being destructive to all or some involved.
Most of the experiences I have had with poly relationships (both my own and hearing stories from other people that are experienced and whose opinions I respect) is that honest communication is key. This should include understanding the expectations of all involved, making sure that everyone is "on the same page".
For some people this comes naturally, for others it's something different, something that has to be re-learned.
"Listen, or your tongue will make you deaf." - Native American Proverb