With that setup, you're allowing each phone to handle 5 calls at a time through out the system. If that's how you chose then very well. I would be careful with the Barge. I don't think the supervisor would like their call barged in on by a regular employee. As for the number of group pickup keys, you don't need that many on that phone. In order for a phone to use that key they have to be a member of that pickup group. Each phone can only be a member of one phone. So perhaps you can have other uses for those buttons. I know it may seem difficult to choose. I don't know the specifics of what you're trying to accomplish for it all.
