ace202 Glad to have you on the board! First, yes, you do have to love the old world style but I would absolutely recommend you invest in some sort of probe thermometer. Just safer that way and prevents the sticks from being overcooked. 100% pork sticks are a good way to go an untrimmed pork butt will have just about the perfect amount of fat for a nice snack stick.
On to the casing question. 19-22mm sheep will be much larger than a pencil, more like a really thick sharpie. If you are looking for something the size of a pencil you would need 15 or maybe 16mm collagen casings. I would recommend you go with the 16mm smoked collagens first as you can buy a 3 pack of them which will be 3 strands and each strand will be 50 feet once stuffed. If you go with the 15mm you will have to buy an entire caddy which will be 50 strands so that would be enough to stuff 318 lb.
Now, you need a stuffing tube small enough for the 15 or 16mm casings to fit over. For more information on what size tube you will need check out the chart near the bottom of the page on the here.
One last thing to keep in mind, the smaller diameter casing and tube you are using the more force that is needed to stuff your product. To make your product easier to stuff make sure you keep it very cold before you stuff it, make sure it has around 25-30% fat content and you can add a little extra water. Adding water will increase your cook time a little but it will cook out eventually and is better than breaking your stuffer!