Travel agents don't have a problem with reduced deposits. In fact, we like reduced deposits if it encourages people to book cruises, who might otherwise hesitate because the full deposit may be too difficult to handle.
The amount of the onboard credit depends on the length of the cruise. The longer the cruise, the more the credit.
Note that the cruise has to be reserved and deposited on October 17 to qualify for the reduced deposit and onboard credit. It has other restrictions, such as not being combinable with stockholders or group rates, etc.