Are there too many languages and frameworks?

As someone who's starting out with a new product (real-estate related), I am looking to choose a back-end and front-end stack. I find it dizzying to look at the choices.

My background, and that of my co-founder, is in C and some C++. We come from a large software company that uses these languages because they are the fastest today (and will probably remain so indefinitely). I would say we feel the most comfortable with functional/procedural languages. Also, SQL feels better than some of non-SQL databases to us. On the front end, we've done lots of HTML, CSS and some JavaScript.

I guess my question to the community is, how do you choose languages/frameworks to work with? Is it based on your career path, i.e. what your employer used, so you became proficient and eventually liked it ? Or on some other preference?

Is there a benefit to trying learn something else? Keep in mind, the nature of our product is such that it will require great performance. Of course the product may flop and nothing will matter, but if it doesn't we'd like not to have to rewrite everything just so we can make it run faster.