This is a slam dunk.. I&#x27;m well versed in both.<p>Use Node. C# is too inflexible and MS SQL Server is <i>always</i> the wrong decision unless a client is dictating it.  I spent 5 years using SQL Server, and when I discovered PostgreSQL seven years ago, it was like a gift from heaven.<p>Node with PostgreSQL gives you NoSQL and structured SQL facilities. Your friend will pick up node quickly if he just stops thinking in C# ways.<p>Designing a web service on Node will be 3x to 4x faster than in C#, and as a startup, time to minimum viable product (MVP) <i>must</i> be your primary concern.  If, after that, he decides to try and write it on his own and prove you wrong, so be it...<p>Cheers and good luck!