Do both. There is a trade-off needed if you know what you want and how you want it. My advice is to seek for guidance from a seasoned Architect or CTO.
What you don’t want to do however is to build everything from scratch. You are looking for speed of execution in the first months of construction of your startup, and your product must be focused on a certain set of features; the underlying technologies must be sustainable and well architected. Why? because you don’t want to be spending your cash refactoring your apps while you are acquiring customers. There is no value in that. This is a core principle of the methodology I built for Startups Construction (AMASE).
If you are looking for guidance, you can send me a personal message on LinkedIn.
