Price List/Opportunity Product Revenues

When our CRM was set up a few years ago, there were only a few product choices that were selected from a picklist at the opportunity level. As we now have many more products available, I want to start using the opportunity product revenues, but I'm running into a few issues.

If I have an opportunity with multiple opportunity product revenues attached to it, how is revenue recognized if one of the product line items closes but the other does not? Is the opportunity revenue updated by reducing by the amount of the closed line item?
If an opportunity has a recurring revenue, how does the opportunity get updated as time goes by? For example, I have an opportunity product revenue with 12 monthly periods of $5k per month for a total of $60k. After 3 months, I have $15k in income, and the total opportunity has been reduced by $15k, and is now worth $45k. How is the total opportunity value updated?