I suggest a quick trip over to the Travel with Disabilities forum where all yourquestions have been answered.
I have been traveling utilizing a wheelchair since an accident in July. I ALWAYS tip the attendant . You can also ask them to stop so that you get coffee and stuff if you need to. I personally dont think you should sit in the exit row. My brace is not even visible at this point and I would not even consider it. Slow = (IMO) not ready and able. Southwest is real clear on this, if you preboard with a disability NO exit row. I have had no issues having wheelchairs ready and waiting for me.