There are tubeless tire "rim tape" tubeless kits that get good reviews in the 650 section. Look over there and see if they appeal.
Usually a tube of "Slime" in a new tube will prevent the great majority of flats from happening. Going to cast wheels is an unnecessary practical expense, with "Slimed" tubes you'll likely never have a flat anyway. The 350 Meteor comes with cast alloy rims, is a better road bike, and the upcoming Hitchcock's Meteor big bore kit will take up any power slack and then some.
Again, lightness requires pricy materials and manufacturing processes. The $4500-ish 411 Himalayan is a great bike for the price, but the KTM, Husqvarna, et al will always be lighter and have more HP. That said, for everyday use and moderate trail bashing the Himi is a great choice. It's likely cheaper to pick up an old Honda, Suzuki, Yamaha or Kawasaki purpose built off road machine if you are seriously interested in off road performance.