Small 5lb flat

Good plan.  I've never done just a flat so I smoke a full packer naked till I get to 195 or so then wrap and into a cooler till serving time. So wrapping the flat to keep moist sounds good.

Sounds good, but I've never found that letting a brisket (or anything else) set after rubbing actually does anything. I usually rub the meat, then go set up the smoker, then put it right in. Letting the rub set will pull some moisture from the surface of the meat, and some claim that helps the rub to "set," but early in the morning I just want to get it in and get some coffee.

When you wrap it, you could also add a quarter cup of a liquid like low/no salt beef broth or even apple juice.  Double wrap in case the foil sticks and tears.