My thoughts:
You look like you prefer coding, so I suggest you try to nail the gameplay first. Use very simple models and levels for prototyping or download them somewhere for free. Don't try to make the game beautiful with fancy shaders or the like, try to make it fun or interesting first.
I would even suggest that you don't use any spec/ normal mapping at all because it always looks like garbage in all indie games and even some big budget titles. Normal maps are fine and sometimes (!) useful and necessary if they are created from high poly models, otherwise they mostly look really bad and give the game a bad and non-unique nor interesting look.
If you have your gameplay ready you can try to create the appropriate atmosphere (not with normal maps) and experiment with an own style. You should try to find one that allows the rather rapid generation of content and don't try to emulate any style/ artstyle that you've seen from big studio.