Can't answer all these questions if only because I don't know your needs, but I am shopping for a color laser currently as well and have narrowed my choices down to either:
Brother HL-2700CN
Lexmark C510N
I also considered the HP 3550N, but have rejected it because HP automatically terminates the toner cartridges after 4,000 copies, whether they are empty or not, which is a dirty trick in my book. The color quality on the HP isn't too wonderful either. Shame, because my last two laser printers were HPs and I got great service out of them.
We have a small network shared by three Macs and a PC, so the networked model is a requirement for us. The non-networked models cost about $200-300 less.
Toner cartridges for color lasers are very expensive. Expect them to set you back in the vicinity $400-500. Also, many of the printers come with "starter cartridges," with about half the toner of a full set. Because of the cost, I plan on keeping our trusty and economical HP LaserJet 5MP in service for most of our black-and-white work.
Some of the printers use Apple's "Bonjour" technology for quick setup (only Brother and HP, IIRC). Since you only do this once, I'm not sure it's a big deal either way. Not a make-or-break issue for me.
Most of these printers are amazingly heavy, in the 70-80 pound range, and all of them are quite tall.
Some of the printers are notably noisy, even when they're not printing.
I'd suggest you go to shopper.cnet.com and look them up. Lots of reviews and user comments.