I am trying power pro this year for jigs and texas rigs. I am a line watcher so I am thinking the hi vis yellow. I am assuming I should be using a flouro leader or can you get by coloring the line with a marker? How much does the uni knot affect casting?

How clear/stained is the water?  If it's chocolate milk I wouldn't worry about it.  Anything else, and I'd want a leader.  I usually keep my leader short enough that I don't wind it through the guides.

No leader , just use a magic marker on the line about 3 ft from the bait.

I use the gold Stren Super Braid with no perceived affect in my catch rate regardless of the water clarity.

When I use a fluorocarbon leader to make the braid sink for weightless presentations, I use the uni-knot connection. Properly tied and tag ends clipped flush with the knots, there is no problem with the knot passing thru a 6mm rod tip. I use 30# braid and 20# fluorocarbon.

In the spring the water is pretty clear but it does turn pretty murky by summer. Maybe I should just experiment with leader length. Whats a good rule of thumb with regards to leader length.