I think it'd be better if the zombies had a 10% odd chance of infecting you from biting/hitting you. Then you have to go find treatment for the infection, or you'll turn into a zombie and all your loot will still be with you.
I agree with these suggestions of yours.. I like the idea of a sort of Role Class type system.. Even when your trying to survive.. Each survivor is bound to have a very specific and detailed role.
A buddy system of some sort would be great. But we should only be able to find each other if we both have GPS... (Not sure if that is in, or will be in the game later though) I would really like to know who my friends are at least.
I have experienced this same issue as well as walking on accessible rooftops and the roof.. and infact.. the whole building would disappear under me.. Freaked me out once or twice. I have my Video memory set to Low.. Since my Graphic's card only has 512MB of RAM.. Seemed to reduce the occurence of this issue.