whenever i add something extra to a circuit i use a clamp meter first to see how much draw is on that circuit, sometimes you find several circuits going thru the same fuse, so it's easy to change things around if need be. try not to increase the fuse size, it's there to protect the wiring not the appliance so by increasing the size of fuse the wire could burn before the fuse blows if something goes wrong.
The fan/light combo's are good for the pandas, not sure if your model had the phono socket on the existing lights for where they plug into. you could always purchase a fan/light combo and add a socket to your old lights (or buy new lights). check the polarity of the lights as well, seen a few where the fan ran backwards
depending on the stereo size (output) you may be safe on a low draw circuit like led's etc, but safer on it's own circuit anyway. for retrofits we try to stick to the roadside of the van mainly due to the antenna not having to go under the awning then. also earth the back of the antenna to chassis (unless it's something like a marine antenna designed to go onto fibreglass) i also earth the stereo chassis. Due to cost restraints we go for the easiest/quickest location unless the client want it in a certain place, so that usually means under a seat facing a door. one other thing i do is take the memory power wire (usually yellow) to the battery bypassing the battery switch, it would annoy hell out of me to keep tuning it every time you turn the battery off.