Mailing lists from raw data

Reposting due to timewaster. :(

We have a Mysql database that holds customer data with an alphanumeric reservation code eg "1234ABCDE".
from time to time we need to select specific customers and notify them of changes to their reservation.
We have a list of reservation codes that we need to lookup up on the database and get customer name and email.
From the list of reservation codes some codes are not in the database or the email is missing.

What we do now:
We query the database and get customer data. We then export data and import it to mailchimp with a specific tag. Reservation codes that were checked but there were no records in the db we keep separate. We create a new campaign and send a message to each contact in this tag segment.

What we need to do:
We need to streamline the process for non technical users.
1. we should upload an excel file that has the reservation codes in one column (one in each line).
2. we should lookup the codes and get the information (email, first name, last name)
3. we should add a specific message for each batch that we upload.
4. we need to import/update contacts in mailchimp, add the specific message in the message body and send the email to customers.
5. We should get a list for the rest of the reservations that were not found in the db.

Further notes:
Each batch can contain from 5 to 500 codes.
We are flexible on the use of mailchimp as long as we dont use our own mail account to send batch of emails.