Casting the heavy, bulky flies can be a challenge, even for the best casters. The nature of trying to hurl a fly like that through the air defies the laws of physics. Mix in some wind and it can be really tough.
Fortunately, most times on the Susky you don't need lengthy casts. A 10-20' cast will get you into fish many times as the fish aren't as far away as you think. When you need the longer casts is when the water clears up and/or gets low. That's when the fish get spooky and keeping your shadow away is imperative.
As far as a sinking line, it can't hurt you, but don't think it's absolutely necessary. A plain ol' floating line with 9' leader will work fine for most of the fishing. If you're trying to get to bottom by nymphing or workings streamers, then yes, by all means getting the fly down quickly would be aided by some type of sinking line/sink tip.
The 9'6" 7wt you have should work fine for the river. For the bass, walleye, etc., it has enough backbone. If you want to go after carp and catfish, then perhaps you might want something more stout as they take you deep and test your tackle.
The best thing you can do is just get out on the river and spend time fishing. Cast away and keep your line in the water. You'll find out what works and what doesn't. If you're really serious about fishing the river, pick up Bob Clouser's book "Flyfishing for Smallmouth". It's a great resource written by someone that knows that river like the back of his hand.
