You can do both at the same time just put the ribs on top. Some people prefer a higher temp for poulty (300+*) to obtain a crisp skin. But when I smoke turkeys, I always brine and cook "low and slow" unless it is a really big bird. If it is a big bird it will take longer to get the meat out of the danger zone (140*) then you want to start off at a higher temp to get the internal temp up faster. Do not cook the breast higher than 170* or you will have a dry product. I pull mine when they are at 165* and wrap in foil and let rest at least an hour. The temp will continue to rise a few degress after you take it off the smoker. I have found, if you smoke a whole turkey or just the breast it is much better after it has set in the fridge over night. It gives it a chance to "mature". Good luck, let us know how it turns out.
