Reg the client interactions

Dear Friends,

Pls clarify the following doubts of me related to implementation project (ECC 6.00).

1. Do Abapers interact with the client? If yes, at what stage in the project.?

2. Will functional people interact with client, at what stage? Is it after customizing?

3. Relating to upload of legacy data from flat file to MM01 txn code (ECC 6.00), can functional people consider fields of MM01 of (4.7 version) for field mapping and not MM01 of (ECC 6.0 version).

Pls help

Regards,

S.Vinod