No need to over think it, it's very simple. Look up a popular 3 star rotation (like Raths), look at the minimum Craft/Control needed, then go to Ariyala, and play with the melds that give you at least the craft/control you have and meld the rest for CP. The only thing complicated is knowing which order or meld or what pieces to meld first but all of that is save on cost (gil). If you want to be cost effective and make your melds more complicated, you'll have to do market research to determine materia cost on your server and slot the most expensive materia to least expensive materia in that order.
