I would suggest you not to choose Blazor. It's not that Blazor is bad or that I have something against, but you don't want to limit yourself when it comes to finding a Blazor developer. You will hardly find a frontend developer who is focusing on Blazor. Today are React, Angular, Vue or similar frameworks the best way to go, especially for a startup where you need flexibility. Keep using .NET for a backend, provide a nice API and implement frontend using already mentioned frameworks.