Let me give you some examples that may help you focus. I don't know exactly which genre your working toward, but many Christian bands use multiple guitars/keys/banjo/etc. in their sound. Listen to Building 429 or Third Day if you want to hear how to do Rockish Contemporary with multiples. Maybe Needtobreathe or Neverclaim if you want to hear how banjo can fit WELL into contemporary music. Obviously you are not trying to sound like Royal Taylor or Gungor with your choices of instruments, but on the worship end of contemporary lie bands like David Crowder and Matt Redman that use acoustic and electric with keys and mixed gender vocals...there are lots to choose from. My examples are all mainstream, but there are literally THOUSANDS of different bands with THOUSANDS of different sounds.
So as far as what sound you SHOULD have, and I don't believe anyone else covered this point: You should sound like YOU! Even if you are doing covers of other Christian music, you should sound like YOUR band doing THEIR music. If you're only in this for doing covers and sounding like someone else, you may enjoy it, but Three things: 1) getting your own sound, 2) (as was stated earlier) defeating your egos and 3) having fun with it, will bring your band closer together and maybe you'll be the next Third Day or Jars of Clay; playing music into the next decade and beyond.
Whatever you decide to do, ask God to bless it and keep Him the focus! Christian bands usually lose out when they lose that vision.