When I was younger we, dad brother and myself, loaded a ton of shells. I mean it was nothing for us to have 15-20 boxes of shells ready to go at all times. Think of it this way. In the beginning just reload what you bought. Powder, shot size, etc. Then decide what you want to improve on. More powder for distance. Hotter powder for distance. More shot for killing or breaking clays. Then just understand the parameters that the shell can hold and the chamber can take. If you think of it a 12 gauge 3" mag factory load is a pretty hot shell. You can then juice it up from there if you want. And really that is the jist of reloading. Doing what you bought or making it better and saving a little money and teaching yourself and kids better gun safety through exposing what is behind the shell.
Greg Luer '85 4Runner, '89 FJ-62