Lets start with, "where do I go to find help?"
I have my favorites I've followed for years, the go to guys that have always be very informative and even more important accurate. I like to start all of my consulting engagements for performance tuning at the Server and disk configuration. If you don't have a solid foundation you won't have a solid architecture. You won't be able to scale as the product grows. For instance, in my current engagement, they don't know if they have a scalability issue or not (they do) , so the work is finding all of the potential issues.
Disk IO is critical to the SQL Server performance. It can be a major contributor to performance problems and everyone talks about it. My favorite bloggers that blog about storage include Wes Brown and Denny Cherry. Both blogs have a wide variety of details about many different topics.
Performance Tuning is one of my favorite topics. If you don't love working on a process that takes minutes to complete and tuning it to sub-second then you're not living. My favorite performance tuning bloggers is pretty huge (and includes Wes and Denny): Grant Fritchey, Paul Randal, Kimberly Tripp (and SQLSkills team), Brent Ozar (and team), and much more.
How about server, windows, and/or database configuration? Here some more (besides the guys above): Linchi Shea, Joe Chang, and many more.
This is a lot of information, and a good place to start. Don't trust just anyone, there are some really bad recommendations out there that will get you into trouble. Stick with the guys that come up with an idea, test it, discuss it and admit when they got it wrong.
The next part will talk about certifications...do we need them? What is their value? How do I start?