I can't offer you any info on the cams, but as far as the other things you mentioned I might be able to help.
Installing a new similarly fashioned exhaust (4-into-2) isn't really going to gain you any more power, although it will probably look nicer than the original 20+ year old system that's on your bike now.
Going to a 4-into-1 system AND rejetting the carbs to match the increased exhaust flow will help, and will also shed about 20 pounds or more of dead weight from the bike.
Every 4-into-1 exhaust system that I've heard is going to be louder than the OE exhaust on your bike. So if that's an issue for you, you're better of sticking with what you have, or just getting a new 4-into-2 replacement system the likes of Jardine or Mac.
Carbs are a diff story altogether.
Larger carbs can increase fuel flow, but without increasing the airflow by installing pod filters and porting the intakes on the head, it's wasted money AFAIC.
Mikuni carbs are mechanically operated, while the Kehein type CV carbs are more of a vacuum operated carb.
Going with the CV's you'd need to figure out where to run the vacuum lines from/to, as well as install a vacuum operated petcock IIRC.
FWIW, installing a decent 4-into-1, rejetting the carbs, and dropping in a K&N or equivalent OEM style replacement air filter is about the easiest and least expensive upgrade to perform. And although it's not going to put your bike in the power range of most modern sport bikes, the power will be noticeable.
One thing to watch for on the 4-into-1 systems offered is that some require removal of the centerstand to install, and also may need to be removed to perform an oil and filter change.
Just read the fine print in the specs on each exhaust system and you'll be ok.