I agree we should go with something we are already familiar with but I come from c++ background and I dont think it is the best language/ecosystem for a team that only have 1 developer. I am a senior developer (c++ as I mentioned) so I think it is not an issue for me to pick up a new language but it is more an issue with finding/training new developer when we need to - I agree senior experienced developer is generally more expensive (or too expensive for early stage startup), so hiring a couple of junior dev sound more efficient but I cannot afford spending months to train them to help them to be helpful, and I feel it is easier to be productive in a .Net environment as Visual Studio is just easy for anyone to pickup.
we have some cost efficient way to get license on Microsoft's software like Windows/SQL Server so the cost on software is not an issue, so is there any other concern with Windows-based solution? you mentioned scalability, why this can be an concern? (I assume windows should be able to do whatever linux is able to provide?)