The hardest thing is product. If you are starting with a product that is focused on non-enterprise users, you aren't going to have product on day one, and often what enterprises need is quite different from what startups or indies or consumers need. So, step one is doing a lot of discovery and talking with the market to figure out what to build.
Beyond that, scaling up a GTM engine (sales, marketing, customer success, etc) is a multi-year effort but it's a bit more formulaic than product, so there are a lot of resources and people out there you can hire to help you with that. Not a strength of mine so I lean on our COO and the rest of the team for that part so I can focus on product.
