We took Rainbow falls to Mt. LeConte lodge years ago. Spent the night at the Lodge. It was amazing. Started a week hike from the trailhead since we were going on to the AT and North.
I was loaded down more than I needed to be(unexperienced at the time). I'm in pretty good shape but the weight of the pack really wore me out. You are climbing a steep incline for a long time. At the time it seemed like it went forever;-> Think it took us about 6 hours.
One thing I wish I kept in mind. Since you hit the falls on the way up, you don't have to carry so much water to get to that point.
Great scenery all the way.
Keep in mind, the weather when you start the climb in will be nothing like when you hit LeConte.
It's pretty rocky once you get about half way up there. At one part the sun was beating down pretty hard and we could hear rattle snakes. We made sure we watched our step. We wanted to see one soo bad but it didn't happen.
It was the coolest thing I ever did in the smokies.