If you rub a chunk of clay across the paint, it will not be effective and probably smear, leaving some clay on the paint. The surface must be lubricated. Most clay is sold in kits with a spray bottle of lubricant, not the same stuff as a detail spray or spray wax. The theory is spray on a section of paint, rub clay gently across paint until it glides across (you'll feel it smooth out), then wipe off the lubricant with a towel. I just found in my one example using the Clay Magic spray that it was not as effective and I still got smearing. A better nozzle or adjustable one that allows a finer mist might work better. Since it is winter and I don't have running water in my garage, I relied on the the spray this time. It worked, but took longer to remove the clay I left on the paint.
Since you are waiting for spring/warmer weather anyway, just wash your Jeep, then clean the bucket/wash mitt and make a new soap solution. Spread the sudsy stuff on a body panel and use the clay. Lots of cheap lubricant that way. Hose it off and dry the whole car when you're done.
As for sealants vs. carnuba wax, they both work. A good sealant is better for most people. Easy to work with and lasts the longest. I have a supply of Zaino products that I'll never use up in my lifetime, but I'd try
Duragloss #105 available through local NAPA stores. TW Ice has a good reputation as well.