Hi Robert,
There are 10 people booked on so far.
For advice on jabs, you're best to check with your GP or on the World Heath Organisation website, just to make sure you're getting the most up to date advice.
In terms of your ESTA, if it's still in date then you're fine to travel, it's not a requirement to go in and update the hotel details.
US dollars are widely accepted, and exchangeable in South America so they should be fine.
Thanks,
Vickie