Hi, I worked on a lot of Android applications that needed native components and fine-tuned communications protocols, so multi-platform apps was impossible or way too expensive. There are a lot of examples over the years of companies beginning with multi-platform framework and finally switching to native e.g. https://medium.com/airbnb-engineering/react-native-at-airbnb-f95aa460be1c
My advice would be, as you are at the beginning of your startup and know React well: Develop your first app in React to showcase your product, add features, remove ones and find your product-market fit. Switch to native only if you have really bad performances issues or features that you cannot implement in React. It will save you a lot of times ! There is very few developers who are experts in Android & iOS !