There's no hidden magic in the playground and in the demo app, we use the same API available for all customers and also the same JS client and best practices available in our docs.

To all your questions, I recommend playing with it in the API playground, you'll be able to test different image sizes, parameters, and have an idea of the cost per inference.

If you have any other questions, say hello on our Discord and I'm happy to help you.

https://fal.ai/models/stable-diffusion-xl-lightning