as already mentioned for that usecase more ram wont make a huge difference if one at all
and the difference between the two ram sticks is that one is a full sized one for desktop pcs and the second is a smaller form factor one for laptops
and they dont have to be the same brand to run in dual channel and theyll always run in that if you have 2 sticks
speedwise theyll be running the same speed (but at the speed the "slower" one is)