For starting somewhere, I'd say a cat sail is a good place, the loads aren't too high, usually no reef points, loose foot is one less bolt rope to stitch, and you generally aren't going out to the middle of the ocean where your life sort of counts on it.
Plus you can compare it side by side with sails of known speed potential and see if you're getting anywhere on shape...on the machine side again, it really helps to have the special foot attachments like the assymetric one for getting tight up against the bolt rope, and maybe a folder for the edging. On the jib, are you going to do hanks or zipper luff? It's hard to sew the two sides of the zip so they are both the same length when you are done, as it has to be separated during sewing. Maybe we should get a whole sewing sticky going...