"Do I assign a number to all of my contacts and use that as a record ID?"
-Nope. Record ID is automatically generated by Method, and cannot be edited or input. Putting a random number in there will cause the customer that actually has that RecordID to get overwritten with someone else's address - (yeah...be careful....this import is powerful but dangerous stuff...).
"aslo, can I export my Customer list, make tons of corrections and then upload it back to Method? Mainly what I'm correcting is address fields - when we put them in, we used the wrong fields and now I have to correct 500 customers"
-Great. Yes, you are fully on the right track. But, now that I know you want to update addresses, you should be exporting and updating *customers* not contacts, since the address fields belong to the customer, not the contact (unless you've done some customization where each contact has your custom address fields - doubt it).
1. Export your existing customers, not contacts.
2. Make sure only select the fields you need to update.
3. The big ahh-ha: make sure you also export the Record ID column. This is so that when you re-import it, Method will know which customer to update. That was the missing piece, wasn't it? :)
4. In Excel, get rid of the rows that have customers you don't care to update.
5. Clean up your addresses.
6. Import. When you import make sure you select the "Update existing records by matching the key fields".
Tip, it is better to save a CSV to import, rather than copy from clipboard, that way any addresses that have commas in them don't screw up the import.
Paul