I have decided.
I think the three post rule was a bit much so there is a change to one of the membergroups, the newbie.
The newbie is what everyone gets put into by default when they register.
The newbie can reply to a thread, and can send 1 personal message, (the minimum I can make it).
Once the newbie makes 1 reply they are upgraded to "new poster" and can reply as much as they like and can make their own topics.