Build our Database of Contact/Account Information

I am the Marketing Manager for a lead generation company. We've been in business for eight years and have accumulated 100's of spreadsheets with approximately 250,000 to 500,000 contact data records (names, addresses, company name, etc.). The spreadsheets are disparate in the headings ("Zip" on one might be "Postal Code" on another). Some may have "Full Name" while others have "First Name" and "Last Name." Some might have information that might be present on that spreadsheet but not others. Some company names are disparate ("Microsoft Inc." might be "Microsoft" on a different record). The bottom line is that we would like to homogenize this data into a single database that we can then easily add to at our convenience. This is what we are looking for our provider to do: 1. Provide advice on whether to use MySQL, MS Access or other database platform. 2. Take all of our spreadsheets and enter the data into a single database. 3. Combine data (if there are multiple records of the same entry) to get the most accurate record. 4. De-duplicate the data. 5. Teach us how to add to the database easily once you are finished OR tell us how much it would cost to have YOU add to it on a quarterly basis, perhaps. 6. Provider must be accessible to communicate by telephone if needed (International providers OK, but English-speaking is a must). Please let me know via PM if I am missing a detail that I should have thought about. If you do a great job, we'll be happy to provide excellent feedback and give you more work, as necessary. Thanks for bidding and we look forward to working with you.