Languages like Python can go a long way for a startup and is my first choice. Rewrite in Rust when it's clear that the API is stable and performance starts to matter.
Exactly. Iterating on an idea is much easier to do in Python, because you can just use lists, dictionaries and sets to solve most problems. Python's string manipulation is also a lot easier than Rust, because you don't have to think about allocations. Once you have figured out what works, you can start defining your Rust structs and enums to build up a reliable code base.