The argument for double chainrings is logical, i.e. less redundancy and weight, but it ignores the pleasure of spinning the largest possible front ring in any situation. In the mountains the 50 will often be too big and the 34 will often be too small, and you'll occasionally wish you had a slightly bigger ring than 50. Doubles make sense for racing but that's about it IMO. Anyway it isn't that big of a deal. If you want to try a double do it, you can always swap out parts later. If going double I would be tempted to order one of those hard-to-find Stronglight cranks that come in a variety of combinations including 52/36. You have to pay shipping from France though. For a cassette I'm thinking you'll regret not having the 11, so maybe 11-32 or thereabouts. I have one of those 29er cassettes on a mountain bike but the wheels and tires are very heavy, I don't think you'll need anything near 36 on a road bike even when loaded. Why not use your FX for touring and get a lightweight fast road bike?