The party is already pretty big and diverse as it stands, and its only glaring thing it lacks is a full divine spellcaster. Any Cleric build will fill that hole just fine, so you can do whatever you want and it should work out.
Since this is your first game, I'd suggest going a balanced approach. A good mix of strength and wisdom, and maybe a reach weapon to complement the Fighter so you're both hammering enemies with AoO's. Cleric is a hard class to screw up due to how versatile and powerful it is; just make sure you raise your primary attributes (strength and wisdom) to reasonably high levels and you should be fine.
If you need more specific suggestions than this, there are plenty of awesome Cleric guides out there that can give you some insight on things like domains, feats, and exact stat distributions (depending on what point buy your table uses)