I only use braided line it has a 0 strech ratio for faster and deeper hook seting also you eliminate memory that mono is so famous for. Look for the power pro brand you can get 10# test at a 4# diameter good stuff it's all I use.
Braided line is great especially for fishing deep water where you need to have little stretch, yes little stretch, not 0 stretch. But sometimes it is best to have a cushion that mono provides. If you fish a lot of cover such as rock and trees braided line holds up better to abrasion than mono. Problems with the braid include clinching down on the spool and also forcing itself down between itself if you have something heavy on the line. If you change it out frequently you should have any problems. For the best mono on the market look for some P-Line because sometimes you need that stretch.
One thing that is important to note is that if you are new to baitcasters mono is better to learn with. Backlash can cause many small knots and mono is much easier to untangle. After you become more experienced with this type of fishing than braided line makes more sense for all the reasons noted above.
use power-pro. quality braid slightly better than fireline (in my opinion). 20 lb test. No stretch is one thing, but no memory is the big thing. You don't want to use mono if you can help it. save that for your spinning reels or you will have way more problems.
Depends on the type of fish and clarity of the water. In clear water you might want to tie on a couple of feet of flurocarbon. A wire leader would be good if you're going after pike or muskie. Otherwise, I normally don't use a leader.
Depends on the water clarity, clear water 130# fluro would be good the high test makes it pretty much bite proof. I am not a strong believer of muskies and pike biting through anything bigger then 100#. Wire leaders would be better for stained water where they won't notice it as much. Depending on the bait your throwing would determine if you want to use fluro or wire. Personally I only use straight wire for WTD topwater and glide baits, everything else I use fluro.
Braid is the best line to use for a baitcaster IMO, if your going to use braid make sure you put some backing on it with mono that is similar diameter as the braid your using, this will help prevent backlashes and having the braid dig into itself. I have used power pro for the last 3 yrs but I am going to switch to something that has more quality control for this year.