There will be monsters in a future expansion pack, yes! First up will be some tile sets, and then more character pieces, including some potential for other races (elf ear heads, etc, and orcs are possible with a green skin tone).
As for your second question, if you want to create more character pieces that work in this style and sell them that's perfectly fine with me! As long as it's your own original work and not edits or re-working what I've made myself. Thanks!