There is more than enough good advice already given, but I'll chime in for the heck of it
I myself am by no means a top steelheader. However, I have been lucky enough to fish many times with a very accomplished Vedder steelheader, who has won the year long derby on more than one occasion. The following is more what he has taught me than what I arrived at through a lot of trial and error.
Leader length: Generally, keep it short! S/h are for the most part not very leader shy. Also, often you will want to fish in tight to shore. I have hooked a few nice ones that were close to shore in 1 foot or so of water. It's pretty hard to fish shallow water with a long leader. For jigs (my favorite) and bait I stick to about a foot. For rubber worms and blades I feel a longer leader gives them better action, so I am probably between 18-24 inches.
Snap swivel: When I started out s/h fishing I used this method. I'd have a duo-lock swivel at the end of my mainline. then I would have a variety of pre-tied leaders on a leader board with a small barrel swivel at the end. To switch rigs no problem, just unsnap the duo-lock, feed in a new leader with swivel on the end, done. However, as I've gained a bit of experience I've learned that generally if one is around and your presentation is proper, it likely WILL smash your offering. I like fishing jigs, a LOT. So most of the time I gear fish for s/h I only fish them. I will take the jig off if I get a hit and then it will not take the jig the 2nd time around, or if I just feel like trying something else. I guess what I am trying to say is find what you like and have confidence in and more or less stick to that. If you like to switch your offering up every 20 casts then I suppouse there is no harm in that.
Leaders: In my opinion you want at least 5lb diff between your mainline and leader. 17-15 is not enough and you run a high risk of breaking off everything if your hook gets snagged. Personally if I hook a s/h I want to play it hard, get it in fast in case it's a wild, don't want to poop the poor fish right out trying to finesse it in on light gear. I run 20 mainline and 15 leader. Also, IMO, and esp for a steelheading newbie, I would NOT bother with the added expense of f/c leaders. If the stuff gives you confidence and you think it catches more fish then by all means go for it. However in my experience, esp with s/h that are not that leader shy, quality mono leader will catch you just as many fish.
Lastly, I'll say that the hardest part about steelheading is FINDING the fish! That is what I struggle with most. Which runs to hit on a given day, if I should go back to the head of the run and hit it again or keep moving down river, and so on. This is what you will slowly learn with time spent on the river. Generally I go out and expect to catch nothing and just enjoy the scenery, fresh air, solitude, talk to a few fishermen and try and learn a thing or two, have a cigar with a buddy, you get the idea. If I do catch a s/h that is a huge added bonus and does not happen very often!!