Sql-server – Install last CU for SP2 without installing SP1 in sql server

I am a big advocate of keeping up to the date with the most recent cumulative update, but only if your testing/QA cycle can ensure full and proper regression testing against it. Glenn Berry of SQLskills is also a proponent of this approach.

Microsoft's own recommendation is to only apply CUs that fix issues that affect you, though they have loosened that stance recently. The problem is that you may be affected by one or more of those issues and not know it, or you might be affected tomorrow even if it hasn't hit you yet. Are you going to go through and try to reproduce the issue behind every single fix in every single CU for your branch? Are you going to do this continuously to make sure you still aren't affected?

I'll be quite honest: I've never had an issue applying any CU to my instances. And in fact their CU release process has been a lot more reliable than the service pack release cycle, and in many cases (including most recently with SQL Server 2012 Service Pack 2), you don't want to apply the service pack until the first CU for that branch has been released anyway. In this case there is an interim hotfix to resolve the issue that wasn't fixed in time to make the Service Pack code, but that isn't always true.

This seems to be a pretty exhaustive list in your question. Service Packs are generally speaking safe affairs - but every so often things can go wrong.

Ideally you would run on a test instance and make sure things are good. Since you can't do that - making sure you take backups is key.

Stopping the SQL Server agent isn't necessary - but if you have many jobs and are trying to make sure a job doesn't kick off just before you start, etc - that is a good plan. Again not necessary, though.

I also like to read the notes on the CUs released after a Service Pack and look for details about potential issues. It doesn't happen all the time, but sometimes a SP ends up breaking something and that then gets fixed in a later CU. In your case you are going with a fairly late release because Microsoft hasn't been generally releasing CUs - only security updates for that product with the current release now 3 versions higher. You can read the list of versions and builds and service packs and fixes post service packs here.