That’s a pretty big question ;)
The answer to the second part is in my video. I mention that someone will copy you no matter what, and how to come to terms with it.
Let’s tackle the first part of your question.
It’s OK to start as a feature and provide a specific use case. You can also decide if you’re building a point tool or general product. Do you know the difference? If you want your feature to evolve into a product, then you need to do customer development and get answers to the following questions:
- What is the problem your feature is trying to solve, and are there additional problems that it needs to solve to provide attract more people?
- Is it an acute problem meaning, people face it constantly?
- Does that solution extend to a lot of people?
- What are the alternative/substitute products that exist?
- Are people willing to switch away from the competition or use your solution in addition to competition?