Babies need all kinds of stimulation. Thats how they develop their likes and dislikes and so on. It is ok to tickle your baby.

Your baby already from the second he was born knew how to let you know when he was uncomfortable, upset, mad, and so on. I bet you know just from his facial expression and the type of cry when he is hungry, tired, hot cold and so on. and I bet you also know when he does not like to be held a cerain way or rocked a certain way or hates those yucky baby spinach and peas, or doesnt want to play with a certain toy and so on. These are the same clues you use when tickling your baby. He will let you know when you are getting too rough or he wants more. Just follow his clues like you do in feeding and changing bed time and so on and you will be fine.