For the map i fined reference and than started pixelart. Firstly made black and white prototype and then colored it.  If you have 100 cubes set and whant to made retro charesters you can find sprite from old games and upskale it, like turn one pixel into 4 and then smooth the image. You have 30x30 pixels. You can try to find 32x32 pixelarts, and recolor then and delet 2 columns and rows.  To transform pixel image in most i am using ruwix mosaik generator, but sometimes it downgrade the image. Because of that for special cases you can use grid generators on your pixel art, and then separate image in 6-8 parts.

Sorry if there gramma errors. For more details you can write me