http://www.hyperdia.com/cgi-english/hyperWeb.cgi can give you a helping hand, you only need to enter the starting point and destination (in your case, i.e. "Shinjuku" and "Tsukijishijo"), it will show up different route, fare and time.
For limousine bus service, it's better to book 1 day before from your hotel to play safe. They will advise you to buy on the next day if plenty of seats would be provided.