I don't know about "expert" but I have made a few pies in my days.
Personally I like the round irons, I have bought them from a number of places such as hardware stores and Bass pro shops, look for the thick sturdy round ones. For some reason I don't like the square ones but I really couldnt tell you why
we use white bread (wonder)with Pam cooking spray most of the time, margarine is good and butter is the best but you have to be careful that it doesnt get too hot and burn. Always trim your crust after closing the iron and dont overfill or they will spit out (practice makes perfect)
These are some of the ones we have made:
Peanut butter and jelly
beef stew (use a can of hormel stew)
grilled cheese
ham and cheese
breakfast which includes and egg, ham and cheese (be sure to cook the egg thoroughly enough, this one takes some practice but the payoff is great)
pizza (use the canned pizza sauce with shredded cheese and whatever you like on a pizza.
any fruit pie filling will work, apple, blueberry etc etc
sometimes we will make entire meals just from the pie irons.