A basic workflow with two options:
1. Detailer pipe (for faces)  + an upscaler
2. Upscaler (with an additional Ksampler) (I use 4X-UltraSharpV2)

For the positive prompt, I've added a wildcard node which populates the prompt encoder. So thats where you add the text.

The workflow uses Anything Everywhere, Fast Groups Muter nodes (Extremely useful and makes the entire thing neat and tidy)

Download models/files from:
https://docs.comfy.org/tutorials/flux/flux1-krea-dev