Hi crossmen,
Concerning the RFC connections, you will just have to change the Unicode parameters of the RFC destination of your BW (SM59 on the partner systems of your BW). No BDLS are to be planned.
Concerning the functionnal tasks, you will have to specify the code page to be used in all the file interfaces (input and output interfaces, infoPackages, program or open hub) and to check the unicode compatibility of your ABAP programs (transaction UCCHECK).
Before the migration, there is not much to do : eventually the SPUMG transaction (mandatory step to be done just before the migration but not so functional) and the UCCHECK (that you can execute before migration to estimate the ABAP work to do).
Regards,
Frederic