You are in the very early stages of being a beginner and you need to focus on the fundamentals and not worry about painting fully detailed realistic renderings, as that's putting the cart before the horse.
Also, there's a disconnect because you don't understand your rough sketches can't progress to fully rendered finished works because they aren't using photo references. That is a necessity, not optional.
And finally, you don't have to use photobashing or Blender to achieve a realistic rendering. I assign my students work all the time that requires them to paint realistically from references as technical exercises. Here are some examples from my students:
All of those were painted by hand, looking are photos references. Most of them were not professional artists--some were just high school kids.
In order to get results with higher fidelity, you need to be much more faithful to the reference in your values, colors, shapes, textures, and edges. Everything you see can be broken down to those components and if you just matched the characteristics of those components accurately you will get resutls with high fidelity in your digital paintings from references.
But I do want to say those were technical exercises, and IMO it's pointless to do digital paintings that can be mistaken for photos because we have cameras for that. The only time I feel that could be a goal is if you're working in the entertainment industry doing concept art and matte paintings that are supposed to make fictional worlds appear real and believable.