My advice then is to finish the "micro" version of the picture, treat it as a study of reference if you will, and only after you're happy with it move it to a bigger resolution. But "detailing" in pixel art is all about being subtle and suggesting things, if you can't do that a big canvas won't help you... Train it!
The small resolution is a lot easier to read too. But since its a dark background, I recommend you not doing it white first -- First thing I personally do is paint the canvas either a middle, neutral gray to help me set the colours (be it in pixel art or regular digital painting) or do a really rough sketch of the composition using only blocks of colors. Sure you can do it with lines but I think you may have a harder time?
Also doing his head facing the camera like that looks a bit stiff, you should try sketching his whole body (up to the hips maybe, but definitely more than the final canvas), his anatomy and stuff, then place his armor on his body. This will allow for a much more natural and well built figure.