Wow. The character sculpt looks great. I would watch the sharp edges you've got on that hand gun. They might be too sharp to transfer to enough pixels for the normal map.
If by any chance somebody need the model, here is a link: https://share.fejes.dev/share/bft_tank Important: this is a high poly model, not game-ready as-is.
Another thing is the sharpness of your edges. Your high-res mesh has sharp, hard chamfers whereas the cube bake you're trying to replicate has rounded, soft bevels.
looks cool, the only crit I can give is the texture is a bit overly sharp. like you went to heavy on the sharpen filter and ended up with sharp noisyness in some areas.
Just one seam going down is all you should need, and the loop around the mouth, because there is a sharp angle there. you need seams at the sharp angles to flatten stuff out.
A WIP girl I'm currently making. Playing with the edge sharpness in blender to get a controlled low poly feel with sharp cartoony features. Gonna see where this style takes me.
Would like to share my script to replace all FBXASC codes to underscore symbol. You can download the script and find all instructions here. NOTE: for now its only works for objects that derives from transform object class
Have you tried contacting Márcio to ask permission and share your progress? Usually concept artists are flattered, and love to see a derivation like this!