This looks really interesting. Big fan of the walking dead series (the first few seasons at least). 

In terms of input, I agree with Rodiak on the idea of having zombies' senses become more dulled as they age/decay. I always hated how on TWD the freshly turned zombies were somehow instantly slow-moving and sluggish. Maybe after people turn they have an initial period where they still maintain all motor function? Having a party-member die, turn, then start sprinting after you sounds awesomely scary.
I like the idea of having everyone already infected through some Corona-esque disease. It adds the suspense of "anyone at any time". Maybe the superbacteria from a zombie bite helps kill the victim, similar to a snake venom type deal.