Brake controller? first. Get a Prodigy. It is probably the gold standard that all others try to reach up to.
The rails may or may not work. Each vehicle usually has brand specific fifth wheel hitch mounting systems. They are not really hard to install, but there are shops that specialize and do it quick and relatively cheap.
As for the wiring? Unless your really handy and have the tools to do the job correctly, you might just go get an extension harness. Plug that into the 7way on the trucks rear bumper, snake it up into the truck bed secure it with a few ty-wraps and plug the fivers pig tail into that.
You did not ask, but since you did mention a 2500 series, just be very careful with choosing a fiver. It is very easy to drastically overload a 2500 with the wrong fiver. Generally speaking a fifth wheel will place about 20% of its actual weight on the hitch. Meaning directly over the rear axle.