question on using more posix threads for server handling multiple client

hi,
I am writing a server application in c in which should handle multiple clients . I have a requirement of all clients will be active they wont disconnect the TCP connection i thought of using (posix)thread per each client and using select(timeout 60sec) in that thread. For example if i have 40 clients all running together client will be communication to server thread every 30 sec server should ack them .and i am exiting thread if select timeout cross certain count or if read byte is 0.

I want to know maximum number of threads(client) that i can run always and Do i need to maintain any thread pool like that for maintating the threads.
I am using Linux kernel version 2.6.31