July for Naadam? Good choice, that's when I went.

A month is not too long especially if you are driving everywhere and not doing any flights. I had a 3 week trip but did some flying.

If you include your interests such as horseback riding, hiking, photography, wildlife, culture, homestays, etc., then more detailed info can be given.

Where to start thread
http://www.fodors.com/community/asia/where-to-start-in-mongolia.cfm

My trip to Mongolia. The trip report starts with a few days in China, then about 3 weeks in Mongolia.
http://www.fodors.com/community/asia/great-wall-sleepover-and-mongolia-trip-report.cfm

These folks used the same company and same guide
http://www.fodors.com/community/asia/mongolia-photo-galleries-up.cfm

An I miss Mongolia thread
http://www.fodors.com/community/asia/i-miss-mongolia.cfm

I spent 3 weeks in Mongolia, and could have spent one more week (if work, and time allowed!) We traveled with Hovsgol Travel for the Gobi and Hovsgol lake portions. We were on our own for visiting UB and Terelj. We also went to Nadaam in UB - quite an experience!

Thanks for the start. We like horseback riding and would like to hang with family for a couple of days to get the nomadic experience. Not really into the whole group tour thing. Probably will hire a car and driver for the gobi. We are also big into kayaking. not sure if there is any water around worth paddling. Really want to see the dunes in the gobi and the flaming cliffs. Also has anybody heard of a cave that has ancient carvings in it that are 700,000 thousand years old?