What's the minimum viable legal protection for a software startup?

Long story short, my tech for activists is almost done, and now I need to cover the legal end.

To make this post as universally useful as possible, I’m going to avoid describing what my own site does, and instead ask: how do you tell if a feature or function needs to be protected? (Feel free to ask for more details if you’d like)

Or can embedding one os licenses into your code, in one place, simply legally apply to all the code in your repo?

I’m assuming I still need to trademark my name and logo, right?

Is there anything else I’ need to do?

How much does legal protection for websites/apps usually cost? And do you have any advice?