Is your goal to run this as a business? If it is you're asking the wrong question.
"What kind of note taking software would you build?" is a question a developer/engineer asks.
When you put your business hat on you need to start asking questions such as "What kid of note taking software would you pay for?" & "How much would you pay for note taking software that does X?"
If your goal is a business & not a hobby (which I assume it is since most people don't borrow 50k for a hobby) you need start asking questions related to generating revenue. You can build the best note taking software ever but if no one is willing to pay for it it will not be a profitable business.