Guineas do a better job of bug control in my opinion, but since they wander much farther than chickens, it's usually best to have them on a few acres or more. A lot depends on whether or not you live in a neighborhood, how your neighbors are (mine are nasty neighbors, and I have six acres) and...
Brooding keets is identical to brooding chicks - same temp requirements, 95, to 90, to 85...etc. The only differences are, you want to start keets out on a game bird starter food - minimum of 26% protein, and put them on a non-slick, non-slip bedding surface, like rubber shelf liner or textured...
I'd start with no fewer than six if I had your setup. Ten is just fine, and like Peeps said, 10 don't make any more noise than six, so I'd go with 10. I hate to say this, but you'll probably lose a few to predators. Go for 10. JMHO
kilsharion, it sounds to me like you have it all worked out well, especially keeping the guineas penned at night. That helps cut down on predator loss a lot. I wish my neighbors were okay with guineas on their property, but (sigh) I'm not lucky that way. They're pretty obnoxious about it , and...
I always recommend that people first do some online searches about guineas - there is a LOT of info about them: care, feeding, cooping, etc., and some people get them without understanding the pros and cons.
I also recommend that they be cooped/penned at night to lessen the risk of losing them...