Download the new SCOM 2012 Sizing Helper Tool from Technet to assist with your new Operations Manager 2012 deployments.
The tool is basically an Excel spreadsheet that requires input on the environment you want to monitor and then returns recommendations based on best practices.
I've tried it out for a few different scenarios and it seems pretty comprehensive and if followed correctly, should make your deployments run nice and smooth from the beginning.
The screenshots below shows the tool in action
You can download the tool from the following link: