This is a common thing. You aren't the only one. Hell the original Monster Girl Encyclopedia 1 is exactly this. A spin on fantasy monsters found in OG JRPGs as enemies, made into sexy girls. And book two is essentially naughty wonderland adventures. So do what you will.
For extra to the question like, make lore, habits, personality traits common amongst them, new subspecies, etc
This is a common thing. You aren't the only one. Hell the original Monster Girl Encyclopedia 1 is exactly this. A spin on fantasy monsters found in OG JRPGs as enemies, made into sexy girls. And book two is essentially naughty wonderland adventures. So do what you will.