replace brake line the damage to the line or if the jb weld gets into the line it will affect how the system works.
I use J B Weld or Araldite for metal to metal.
A good epoxy will join metal to metal. I use Ren-Weld and J B Weld with a lot of success. Autobody shops use an epoxy called Speedgrip -very expensive !
If you are replacing the brake lines ( metal ) then just use your better judgment. They do not have to follow the original route.
Pot metal-no. Better to use jb weld or something.
To support the molten metal while it is cooling
You would use 316 as the filler, it is the more pertinent metal of the two.
I always prefer hard metal lines, less possibility for issues later. Bend the excess metal line around a socket of appropriate diameter, that will ensure it bends smoothly without kinks.
I wouldn't. Replace or repair the line instead.
NO!
Solder is a metal ,specially alloyed to be used to fix or weld together other pieces of metal. How to use it would depend on the application and the exact metals being used
You can use the 308 or 316.
Weld or solder them, or use screws, bolts, clamps, or rivets. Gluing with epoxy is also an option.