I'm trying to figure out the best balance without ruining current relationships.
OTOH, I officially let my chain of command know about my project last week (per company policy). I put it off as long as ethically possible because I do not have the same level of trust in them (also from experience). I do not know if there will be any repercussions.
If you trust (really trust) your supervisor, let them know. They'll appreciate it, and your team will thank you. If you don't, then don't. If you have IP agreements or other legal entanglements that they could use to destroy you, find someone with experience in those areas to advise you on a best path forward.
FWIW, I think most YC startups share their employee contracts, and in it, there's a section that mentions you are entitled to your own IP as long as you give notice of the side project AND you don't use any company resources on it (like working on company time, their laptops, etc.).
The University that employs me as a day job requires that I disclose any additional sources of employment or potential conflicts of interest... by that logic, I think I am obligated to disclose it. I do go to great lengths to make sure that I'm not using any University resources, don't do any work on the project while I'm there, etc.
My direct supervisor has always known that I develop apps on the side, thinks it's cool and it's otherwise not a big deal at all.
I think it's all about how much time it is taking and how you portray it. Is it a side project/hobby that you happen to make money on, or is it a fast-paced startup that you're spending 60 additional hrs of week on? Also, do you expect to have to leave your position soon, or are you still in for the long haul with your day job?
And yes, anyone with a manager like the one you describe should absolutely run for the hills :)
She doesn't encourage it, nor discourages it. It is completely disjunct from what I do for my employer. And maybe somewhat intriguing, I don't know, she's just never asked for more information.
There's no reason not to hid something that shows another side of yourself, be it art, technology, business, trade, psychology, whatever. Assess the relationship with your colleagues first.
Heck, I had some colleagues that would regularly miss meetings because they were volunteer firefighters. That never caused them any shame.
Assess the conflict of interest. If there is none, declare it. If there is, then tread carefully, because you may be violating a contact you agreed to.
Then again, my side projects are more in the vein of, "Find security holes in Symfony," than, "Start a multi-million dollar enterprise."