I recommend you keep working with a small scale so your don't get overwhelmed
Look how much more detailing I could get out of that smaller knight:
Stuff I considered:
Body shapes
How medieval armor looks (look up references!). A chest piece isn't a flat board
Reflectiveness of metal
Direction of light (light that is coming from the top-left here) and back-light (from the right)
Btw don't mix resolutions. In that 128x128 pieces you're putting down 2x pixels manually, but also some stray 1x pixels. That's the ugliest and most absurd thing you can do in pixel art IMO. If you're doing 2x pixels might as well work with 64x64 and double it up when you're finished
Cheers