A straight clamp might can come in handy, but I mostly use helical. I mostly fletch with feathers too. If you think you'll do feathers, at least sometimes, you need to match the helical to the feather. It doesn't make sense to set up for feathers that you can't get locally, so check your archery shop and see whether it stocks left wing or right wing feathers. Then buy left helical for left wing or right helical for right wing.

For vanes, it doesn't matter. Left, right, straight. They're freakin' plastic and will twist and turn any way you want. In fact, that's a test question I use when I go to a shop I've never been to before, to see if they know their elbow from their forehead about archery. Pick up a pack of vanes and ask 'em if they're left wing or right wing. You'd be surprized at the number of archery shop doofoids I've busted with that question.

Even with vanes though, and regardless of rest type, Ivery muchprefer helical over straight offset.