Arun,
There is no sense is going for a wide macro lens and trying to couple it with a teleconverter. You are already using a 40mm macro. It is a short lens and one needs to be very close. I find a lot of subjects feel threatened when my lens is close to them. Whatever light would be available would be blocked by the lens moving close. I personally face a big challenge in filming macro subjects as the camera and lens has to move very close. If not, the macro subjects become like very wide angle with the macro being small in that frame. If that is what you need, then just user your 40mm and shoot. Why buy another lens?

Where do you expect to use your ultra-wide angle lens? And how frequently?

I don't have much info about laowa lens.

Cheers,
Sabyasachi