What type of overloads should I install

If you like adjustability, go with air bags. You will have to adjust the air every time you hookup or unhook the trailer, and you have to maintain a minimum air pressure at all times or risk damaging the bags. Also need to be aware when jacking or lifting the truck, if you do not install limiting straps or lift from under the axle, the bags could be damaged when the axles droop.
I had air bags on our last truck and enjoyed the adjustability, but on our current vehicle I chose timbrens for less hassle and zero maintenance. The install was easier too.