What do you plan to do with the bike? The stock windscreen is excellent for track work. There are double bubble screens for more protection if you plan to ride long distances with it, but since you have a Sprint, that's probably not the case. I would start at Lockhart Phillips, but that's partially because they are a sponsor when I actually manage to race a bike (there's the disclaimer). There are a number of other excellent sources for that kind of thing, so it boils down to personal choice. As far as exhaust, an aftermarket slip-on will remove quite a bit of weight from the back of the bike and from up high. Once again, the specific one is a matter of personal choice. Zard makes an interesting low mount full system that exits just behind the rider's right side peg. Otherwise, any full system you get will be in a location similar to stock. Whether you use a slip-on or a full system, you will have to find a way to remount the license plate and turn signals. When I put a Jardine on my bike, it came with brackets to carry the plate and signals. I can't say what other manufacturers do, since I have no experience in mounting any other can on my bike. This is another personal preference thing, and I don't see any reason not to shop around to get the best price once you settle on what you like. A specific brand of exhaust is what it is no matter where you buy it.
It's a squid thing. You wouldn't understand.
Go soothingly on the grease mud, as there lurks the skid demon.