Little update!!
I've sculpted the lower body where the limbs connect:
Pic 1: I applied clear tape under the main body/shell and sculpted the lower body according to the painted patterns.
Pic 2: The clear tape serves two purposes. First, I can see the pattern, this allows me to sculpt the lower body to the desired proportions and get a nice match between the two parts. Then after the new part hardened, it doesn't bond to the main body and I can separate it. (If there's another or better method it'd be good to hear about it )
Pic 3: Both parts separated.