I am thinking to install the new VC update 4. Any suggestions before I install it?
backup your DB, because it will require a schema update.
and note KB's http://kb.vmware.com/kb/1008296 and http://kb.vmware.com/kb/1008330
backup your DB, because it will require a schema update.
and note KB's http://kb.vmware.com/kb/1008296 and http://kb.vmware.com/kb/1008330
Also, disable HA on any clusters.
I am going to stop the VC services before apply the upgrade, so I guess no need to manually disable HA?
You should still disable HA. HA is not dependent on vCenter, only configured through vCenter. But I have seen HA issues if it remains enabled when the updated vCenter comes back online. It is just a good practice to disable HA.