[kelnos]

Related to (a), if you do want to start your side business in the same industry as your employer, you must clear it with them -- in writing -- first. Yes, there are many many situations where they will laugh and say "no", but you never know.

For example, I work at Twilio. Let's say I hypothetically have some ideas of things to build on top of Twilio that I could turn into a side business. Maybe these things are features that Twilio might want to build into the platform, or maybe not. If I wanted to start a side biz doing these things, it'd be in my best interests to clear it with Twilio first. They might say "that's out of the scope of anything we'd ever build into our product, so go ahead". Or not.

You don't want to find out several years later, when you're becoming successful, that your old employer has decided to stake a claim on what you're doing.