I have a 7-quart and love this size. It holds the larger chunks of meat and a few veggies just fine. Also, a larger, tougher bird fits nicely too.
You will not be disappointed!
I have a WMF right now. I miss my old one terribly (I do believe it was a Mirro). It had a rocker valve that I truly miss with 5#, 10#, and 15# "holes". The sound alone can make a day better.
My advice is to: Whatever you get read your instruction manual. Know what the safety features are and then don't "taunt" them before they are ready to release. Know what a slow release is and a quick release. I always use my quick release method (all that means is taking the entire unit and sitting in your sink and running cold water over it until the pressure is fully released).
We have lots of recipes to share and there are lots of good cookbooks out there. The Internet is FULL of recipes.
How big is your family? That will help also in determining the correct size you need.