1. Noticeably louder, still quieter than my weed whacker.
2. Yes, no problems with the center stand. Although I could never get the front tab to mount onto the head bolt.
3. Depends on what other mods you have planned and how fast you want to go. It's a pretty good pipe for the price, but you might only get 5 mph more with it, depending on your current setup. I got mine around the same time I rebuilt the motor, got a 13:13 carb, and ported the intake, and those together got me from a 27 mph top speed to about a 37 mph top speed. Keep in mind this is in Denver where there's less oxygen, so if you're at sea level it will go faster.
Whatever you do, get a set of jets (probably in the 60s range) and make sure it's all tuned up and running properly. Also make sure your gaskets are intact and not leaking, and your points are cleaned and gapped properly. Even with the Malossi airbox you'll need to upjet a little bit.
I should also add that after a couple thousand miles some of the rivets holding the baffle (muffler) onto the pipe started to wiggle and round out the holes. And I ended up painting the pipe with BBQ paint because the clear coat burned off and the pipe rusted pretty quick.