I've made a couple pairs of turnshoes and didn't use lasts or supports and they turned out fine. Considering it's a 90 degree angle on the leather before turning, I'm not sure how you'd support it. I run a stitching grove on both flesh sides and pre-punch the sole (edge-flesh) then stitch the upper to it (flesh-grain) while both are wet so it stays nice and tight.
For patterns, get yourself some really cheap vinyl and sew it up on a sewing machine and make sure it's pretty lose especially over the top of the arch. You'll want space for a felt insole.
After turning, a pair of the inexpensive cedar shoe shapers are handy to make them fit nicely.