Hey Heath, you are on the money here, power to cap then amp, as for the negative it shouldnt matter if you give it a seperate earth or not. You are also right about an accidental discharge, there is a lot of potential energy stored in them and they are designed to discharge very quickly, hopefully the worst thing that would happen is that it would scare the sh*t out of you -keep that in mind when you are removing it too, they will stay charged for days after being unhooked from the battery.
Also, they wont stop your battery from going flat as they only store charge that is already there, they can not create power, cheers