1. I found my first few clients literally through happenstance -- people were describing problems they were having with enough clarity that my 20 years of dev experience made it fairly clear that the problems were recoverable. Now, I mostly find customers through referrals and by attending networking events and talking to people who sound like they have both money and problems.
2. My customers have the expectation of confidentiality. I will make these generalizable statements though: understanding ORMs and understanding SQL are related but not identical; CAP is hard; picking keys is hard; confounding your data model and your interface is painful for users; sharding is hard; pick UX libraries based on how consistent they are not on how new they are; developers that are producing 10x the code may not be producing 10x the value; if week on week, your project is consistently n/n+1 * 100% done, you have a estimation problem and just the fact that you're agile doesn't help with this; the whole point of tags was that not everyone agrees on categories; queuing theory is real; your spreadsheets aren't as consistent as you think; the fact that an engineer can figure out the bigO of a sort doesn't mean they understand efficiency in real life.