Is it legal to send messages to bitcointalk users for advertise and marketing?without my account suspended.
It is legal, but not every user will welcome your message. Most of them will probably ignore it.
Consequences will depend on the admin. If many users will report regarding your message, then the admin will take action.
Is it has a limit number for messages i can send?
Yes it has, it is to limit newbies to send spam messages to other users.