To move the existing systems to MSSQL 2012 and Windows 2012, the systems should have the minimum SP level. For the ERP system there is no need to do a system copy at first. I would get the DB upgraded to 2008 on the existing server and start CUUC (Combined Upgrade & Unicode Conversion) to upgrade the system to EHP7 and also get UC done. When you do CUUC and export will be taken. In order to reduce the downtime of this operation, you can install MSSQL 2012 in advance on the target server with Windows 2012 and make use of the parallel export and import to reduce the downtime. For the BW system you will need to split the stack if the target system should be based on NetWeaver 7.4
RB