Microsoft recommendations on scaling out Search components

I’m currently preparing to take the 70-332 exam (Advanced Solutions of Microsoft® SharePoint® Server 2013) and suspect there may be questions relating to Search Service capacity planning.  These are the Microsoft recommendations for scaling out the Search Service components that were including in the 20332B course material:

• Deploy and configure one additional index partition per 10 million items
• Always use two Query Processing Components for redundancy
• When you have more than 80 million items, increase the number of Query Processing Components to four
• Deploy and configure one additional crawl database per 20 million items
• Deploy and configure one additional link database per 60 million items
• Deploy and configure one additional analytics database for each 500,000 unique items viewed per day or for each additional 10 million items
• Always deploy two Search Administration Components for redundancy