Do i need to bring my lo to visit preschool before decided which one for her preschool?

It is not a need. It is up to you. No hard core rule. Whatever that makes you feel comfortable is more important than all else.

Yes for me. I would bring my LO to 'feel' the environment. And if possible to see how the teachers interact with my LO

It's up to individuals, but I would, so as to see the reaction to the school environment and the Teachers..