Scalable API is not about the language or framework. It's about system design. If you wish to scale, you have to know how to design to scale. So research and read up about system design, it comes down to knowing how to cache, how to use queues to take off load off your API, deciding on async and sync operations, understanding distributed systems, how to split work and data across systems. Understanding when to use NoSQL. On practices, good software engineering practices apply irrespective of if it's an API or desktop software. On frameworks usually don't, especially to ORMs. Most frameworks are heavy, but if you must, then use what's battle tested and avoid the new shiny things.

Books - designing data intensive applications, any good book on queueing theory. Blogs - I believe are the best, Netflix, Facebook, Google, Uber, any of the big companies that share how they build their systems, you will pick up plenty of knowledge. Some talks from conferences, like Qcon & Strangeloop, Oreilly Arch.