I keep two back up spools with braide line for a couple of my spinning outfits. I use only Berkly fireline and it works great, I dont use it for everyday use though, just special situations. You have to make sure to put it on the reel the way they put it on the spool. To do this start your reel, go a couple turns then stop and look, if the line wants to come off turn the spool of line the other direction. If you start with the bottom of the spool faceing up and the line isnt going on right, turn it over so the label shows.
Now as far as flies, braided line floats, so keep that in mind, ribbing should ok, but if you are tying a wet or a nymph you'll have to weight the fly.
Leaders out of braid? NO its very limp and wont lay out right. The only time I had luck with this was bass fishing heavy cattails and lilly pads. I used a very heavy mono 40lb(4') to 30(3') lb then a short 2 foot section of 20lb braid. It worked great for pulling big bass out of thick stuff, and casted decent with only a 2foot section of the braid.
Good luck
Bear