Bartcanoe, we will probably be camping at about 9,500-10,000 feet elevation so it will be cold in the mornings/evenings (probably down to about freezing), but during the day it should be up to 60s or 70s. Sept. is a beautiful time to be in the high country. I recommend a 0 degree sleeping bag-synthetic or goose down but with down you have to keep it dry. Most years, we get short-lived afternoon thunderstorms but sometimes, we'll get a storm that moves in for a few days and camps out so some sort of rain gear will be necessary. You can go as high-tech or low tech as you can afford. I like wool and then a poncho for afternoon showers, but I also have a Gore-Tex jacket in case it rains a lot. Hope this helps.
As to whether you can learn enough to hunt elk effectively, I've hunted elk since 1986 and still consider myself a novice. I learn something new about elk every year and just when I think I've got a sure-fire way to take an elk every year, they change their "pattern" and aren't where they should be. That's what makes elk hunting so challenging, frustrating, fun, and incredibly rewarding if you can get one on the ground, esp. on a public land DIY hunt.