Yellow PP or PP Super Slick on all my reels, and leaders always.
Materials? Take your pick. I like Yo Zuri Hybrid, Gamma Edge FC,
and others. Typically 6, 8, or 10lb test, but have gone down to
4# and up to 15#.
As @Team9nine said, find a connector knot that you can tie
consistently, easily. Knot arguments can sometimes rival religious
arguments for intensity, LOL. Personally, I tie uni-to-uni most of
the time, and the Alberto/Mod'd Albright the rest. As long as you
have considered your kit (rod, reel, drag, line type, etc.) you
should be able to handle any freshwater fish.