There is no definitive answer to your question, since it will totally depend on the complexity of SSIS packages, SSRS reports and SSAS Cubes.

Doing in-place upgrade is always risky, since if something goes wrong, it would be difficult to rollback. A side-by-side migration is always a good and reliable method, since if something goes wrong, you already have a system up and running that you can point to.

Always, test, test and test your migration and have a fully tested rollback plan. Use upgrade advisor (this touches DB Engine, SSIS, SSRS and SSAS) and fully address all the issues raised by it.

• I have written a thorough answer for database migration and post restore steps
• For SSRS migration, I have written it here.
• Devin Knight talks about Upgrading Packages to SSIS 2012 and msdn has a whitepaper on 5 Tips for a Smooth SSIS Upgrade to SQL Server 2012
• For SSAS, this method should work in your case as well.

There is no definitive answer to your question, since it will totally depend on the complexity of SSIS packages, SSRS reports and SSAS Cubes.

Doing in-place upgrade is always risky, since if something goes wrong, it would be difficult to rollback. A side-by-side migration is always a good and reliable method, since if something goes wrong, you already have a system up and running that you can point to.

Always, test, test and test your migration and have a fully tested rollback plan. Use upgrade advisor (this touches DB Engine, SSIS, SSRS and SSAS) and fully address all the issues raised by it.

• I have written a thorough answer for database migration and post restore steps
• For SSRS migration, I have written it here.
• Devin Knight talks about Upgrading Packages to SSIS 2012 and msdn has a whitepaper on 5 Tips for a Smooth SSIS Upgrade to SQL Server 2012
• For SSAS, this method should work in your case as well.