Switch number and content from 3gs to 5

I have had a 3gs forever. Bought husband a 5 a couple of years ago and he decided he didn't like it. (He wanted a bigger screen.) So he bought an android phone, and the 5 went into the desk drawer. 3gs is giving me fits now, so I want to change phones. The SIM cards are two different sizes, so I can't just switch them, but I do already have an active AT&T SIM in the 5 associated with my husband's number. What do I do to get my number and content to the 5? Do I just do a factory reset on the 5 and then back up 3gs up to the cloud & download to the 5? Will that move my number along with contacts and apps? Is there something else I need to do? Our local AT&T store doesn't keep very good hours, so hard to get help there. (Closed after 4:30 AND closed weekends.) I would appreciate any advice.