Upgrades can be tough if they are not planned well. Event in very good planned upgrades there are some issues but the idea is to be prepared to squash them on the moment and finish the upgrade process to the end. This is what one of the Microsoft teams did when they upgraded their SCSM 2012 environment to SP1. read about their experience here.
The final version of Infrastructure and planning guide for System Center 2012 Operations Manager is available for download. The guide will help to architect and design you SCOM 2012 infrastructure. Download is available here.
On his blog Anders Bengtsson explains what are the key points in estimating the Orchestrator database size. If you are planning to install Orchestrator in your environment read Anders’ article so you can estimate the database size