However many U-bends you think you need, add at least one more. I cut my pieces in a band saw and then sand until it's a perfect fit. I found that I didn't need nearly as much straight tube as I had ordered because of the "legs" of the U-bends. Start from the manifolds and work your way back, tack pieces together so you don't have as many that you're juggling.
Have fun, and enjoy that you're not paying for kink bends and routing that's not quite what you wanted.
Oh, and since you mentioned Summit don't bother buying the band clamps with the holes in them for tack welding. Those only work if you're connecting two straight pieces.
