Re: why are there so many users in my system ?
The primary reason for having lots of different "users" on a Unix machine is for security. You can give users or groups limited privileges and they are less likely to wreck your machine. An easy to understand example of this is the "admin" group. Users not in the admin group aren't allowed to use the sudo command (and, if they try, it logs the attempt). Having lots of users with varying permissions allows a very fine grained control over what a particular "user" (even if that user is just a placeholder for a process) can do.
Don't try to make something "fast" until you are able to quantify "slow".