We have a 12" and a 18". IMHO you need two Dutch Ovens (AFAIK the dutch ovens you get in most cookware kits are just stew pots, a true dutch oven has the three legs and rimmed lid, read the Foxfire books
).
IMHO ther are two ways to use a Dutch Oven, as a slow cooker and as an oven.
Slow cooked Pot roast:
A chuck roast large enough to feed everyone, about 1/2# per person.
Potatoes, carrots, onions, celery stalks, one each per person.
One can of stewed tomatoes.
A bay leaf or two, salt & pepper.
Throw it all in the oven. peel the vegies if you like or just scrub them good. You can cut them up to, or not.
Find a gravely dry creek bed, dig a hole about twice the size of the dutch oven. Put a couple of shovels of hot coals from the fire in the bottom, put the oven in, fill the top with coals. Fill the hole with gravel. Go for a hike, or fishing, or whatever. This is one of those things that is hard to over cook but give it at least three hours to be done. A whole lot less work than fussing with store bought charcoal for a meal that takes a long time to cook.
For the bisquits I follow the Bisquik directions for rolled or drop bisquits. As Cruiserdrew mentioned use 2/3 on top and 1/3 on the bottom. I use a cake pan on a cake rack inside the oven and preheat the oven before I put the bread in. This allows you to remove the bread and start a cake or other daesert without a cleanup. I think there was an ephiney moment for me when I decided to started using my oven as an oven rather than a pot. Any kind of baked good will come out better when you use a internal pan with a rack under it, the air gap reduces hot spots. The pan allows you to start another course without cleaning and re-heating.