Pond plants in containers or planted out?

I have recently had a pond dug into our clay soil. It's about 7m x 10m at the widest point and I'm hoping to make it into a low maintenance wildlife pond. A book I read said to plant all the pond plants in containers to stop them spreading too far and to make them easier to divide. However I'm going to need a lot of pots! If I go with the stated spread of each plant will it still become a jungled mess in no time?
Thanks!

 

We started off with our plants in containers but they still outgrew them at a stupid rate and were difficult to divide and separate so now they are loose and can be divided as necessary.