Software that supports a lifestyle business is typically different than YC scale or ideas accepted by YC. If your goal is to build a lifestyle business that affords a salary of ~$100K, you likely don't need to scale beyond $1M in revenue.

You would actively want to avoid raising money (from YC or other investors) because their goals are to get companies to $100M+. That isn't a bad thing — it actually opens up the door to a much wider range of problems & niches, with more flexibility & less pressure.

1. Given the above, scrap the YC aspect of the question. But ideas can come from your own experiences with problems or pain points you felt. Or can pick an industry or role and have conversations with people to find common issues or challenges.

2 & 3. This depends on the vertical & industry you serve + their role. If you're selling to VP of sales of startups, can get by with emailing + LinkedIn. If you're selling to local professional services, can get by with cold calling. Where you build your list will depend on your target.

Selling to owners of < 10 employees) is very different to < 100 and so on.

If your business is tiny it can be hard to sell to a business that is large. The larger the business the more they evaluate your business as a potential long-term supplier and less about the product.

As you are starting out I recommend talking to smaller, rather than larger businesses.