ECC 5/MSQL2005/Win2003 to ECC6/MSSQL 2012/Win2008 upgrade

Dear All

We are planning to Upgrade from ECC 5 UC running on Win 2003 server with SQL2005 to ECC 6.0 EHP 7 UC with Windows 2008/ SQL 2012.

My Understanding is that direct upgrade to ECC 6 EHP 7 is not possible . The Solution we are thinking is Two step upgrade

1. Upgrade from ECC 5.0, SQL Server 2005, Windows 2003 to ECC 6.0 Ehp5, SQL Server 2005

2. Upgrade OS to Windows 2008 and DB to SQL Server 2012

3. Upgrade ECC 6.0 Ehp5, SQL Server 2012 , Windows server 2008 to ECC 6.0 Ehp7 , SQL Server 2012, Windows Server 2008

Here are my questions

1. Is Sandbox upgrade must for both upgrades , Since after the first upgrade we are already on ECC 6.0 EHP5 , IS it necessary to perform Sandbox upgrade for second upgrade(Sno no 3 above)? , Can we start from DEV? If yes what are the risk associated

2. Is there a 4 weeks cooling period required between Step 1 and Step 3 or Can Step 1 and Step 3 be done over a weekend at one shot?

Will we be able to complete both upgrades on the weekend, The Database size is only 400 GB

Any quick help is appreciated. If any of the experts can call me on my mobile i can explain better

Regards

Deepak

+91 9841506070