Pokemon question; Mew?

I currently just started playing yellow version and i know how to catch mew but i need good advice...should i keep him on my team? i mean is he strong enough for the elite four and the other gym guys before them? i plan to have the 3 starters and pikachu what could my other 2 be ? i realize that i asked a lot of questions but if someone could answer them then that would be really helpful. Thank You.