Are there any limits on how many messages that can be sent?

This article details the limits associated with the Walution extension.

There are no limits imposed in Walution regarding how many messages that can be sent in a given license period.

However, Walution sends messages at a maximum rate of 5 messages per minute. This means that a maximum of 7,200 messages can be sent in a 24 hour period.

This send rate reduces the chances of your phone number being associated with a spammer, and it helps to avoid your phone number becoming blocked. 

Nevertheless, there is no guarantee that your number is not going to be blocked. If you send thousands of messages of the same text, WhatsApp may still block your number.

Each user on a team license can send messages from a maximum of one WhatsApp phone number at a time.