Yes you can use a mixer with multiple mic inputs. It helps to have matching mics, but not essential. If more than one person is singing at the same time, don't use the vocal harmonizer.
I find it's more believable on a lot of songs to use the simple vocal harmonies, such as duet, rather than the choirs. Use the harmonizer sparingly--it's easy to overdo it.
I find the factory preset mic e.q. works quite well with SM58.
I've tried just about every mic there is on the 2000 (and others). Most of the time you can e.q. any of them to sound good, but individual voices may sound better with certain mics. Only way is to try them out.
I tried a head-set mic that Gary Diamond loves, but couldn't get it to sound like I wanted for my voice. Gary sounds good on it though. I also missed the dynamics of moving away and closer to the mic, including the proximity effect.
DonM www.donmasonmusic.com