[Workflow] How to design a model: texture vs (Material/Shader)

I was wondering what is the ideal way to create a desired model;

Consider a simple example ( e.g. https://previews.123rf.com/images/rasslava/rasslava1306/rasslava130600660/23397189-Water-Sphere-isolated-on-white-background-Stock-Photo.jpg ):

How would you make that model? Texture only? Material (with colors) only? Both?

My initial guess would be to use both - but if so, where is the line between texture and material? which parts of the look are from the texture, and which are from the material? How would you decide it?

Depends. On your particular picture, it looks like it would make sense to use normal map, while accomplishing everything else with material nodes. There is no distinction answer for your second question. Eventually you will learn to feel, which path to take where, but most likely you will have to learn by trying.

Thank you for your answer!

Just to understand - why did you decide it would be better to do use normal map with material nodes?
why wouldn’t a texture be good enough for it? what would be lacking by using it alone?

Also, as a second example (just trying to understand better) - how would you acomplish a fire character like this: ( https://upload.wikimedia.org/wikipedia/en/c/c7/Human_Torch_(Johnny_Storm).png ) ?
(I’m assuming this is gonna be a bit more complex, since it might involve fluids/particles ?)

Quick response to your second question, you would spawn flame particles over the mesh. UE4’s particle tutorial series covers this in one of their videos.