The biggest thing I can say is don't underestimate underwriting. There's a reason a lot of carriers focus on specific areas. There's a hidden customer acquisition cost in that a group of new customers that has a bunch of bad business that needs to be weeded out.
If you think about it a customer knows their own risk better than anyone. So, you're betting that you can judge their risk better than them and your competitors over and above your cost to manage paperwork, regulations, money and fraud.
This is also why carriers like agents so much. Agents effectively act as a first screen for carriers that allows carriers to turn away customers in a way that they can't legally do through their policies. Ie "encouraging" agents to send business from certain neighborhoods to other carriers or agents.
This is a discriminatory practice but every carrier does it because it's a way to circumvent the public nature of their filings, and it's another hurdle that startups will need to overcome, particularly if they're doing online distribution where adverse selection is a more pronounced risk.
If you think about it a customer knows their own risk better than anyone. So, you're betting that you can judge their risk better than them and your competitors over and above your cost to manage paperwork, regulations, money and fraud.