No routing need for 6-string EMG pickups. There's only some routing needed for 7 string EMG pickups since the pickups are housed in bass pickup housing. Dunno what you mean regarding the circuit though.
Well, SOME 6 string guitars need routing to fit EMGs (RGAs, for instance) but any guitar with pickup rings won't have any trouble. All the electronics will have to be replaced with EMG electronics but it should all come with the pickups if you buy them new.
EMG's have sharp corners. Some guitars, even with mounting rings will not fit an EMG because the route is rounded at the corners. Also some guitars have a shallow route, and the EMG's are rather deep. But all the Korean routes, including the RGT's are oversized, and they will fit EMG's with no problems at all.
Yes, you should replace the tone and volume pot along with the input jack. As I mentioned before, if you buy the pickups new then they'll come with all of that and you'll just have to install it all (or have a professional do it because installing EMGs can be a little tricky).