haha oh yeah. Exotics can drop at any LL depending on your own. From what I've seen they'll decrypt as high as 6 LL above your character. I got a 326 Zen Meteor when I was 320. So theoretically you could maybe get 335 exotics once you hit 329 but I haven't personally confirmed that.
Yep, you can run it as many times as you want and get rewards at the end. Legendary ghosts, class items, and the PoE exotics (Lord of Wolves, Dreg's Promise, Queenbreaker Bow) all have a chance to drop as activity rewards. They can even be max light gear depending on your character's light. I've gotten two 335 ghosts and a 334 Lord of Wolves from my 4 Challenge of Elders completions.
edit: you can also get legendary engrams but these will be capped at 310 light max like all legendary engrams.