Your idea of transformation is not feasible! The anti-theft net is just a few bolts fixed on the wall, and it can't bear other weights except its own weight. And after you see them, it's the last straw!

Obtain property consent

The bay window changes the facade of the building, and you must obtain the consent of the residential property (even the planning department) before you can act. Otherwise, it will not be worth the loss to restore the original state.

If the structure allows.

If the structure allows (I dare not say that it can be done before I have seen it on site), I can remove the wall under the window from the ground and float it out, and make a glove box below the height of the window sill (the other three sides must be made of concrete walls and must be firmly connected with the original wall). Use the original window and add a fixed window to the empty part below (the second point you mentioned), so as not to waste the original window and ensure safety.

Specialty construction

The above two passed, the realization is actually very simple, but it must be professional! We have a team that specializes in transforming smokeless stoves. They can help you finish it. I wonder if you have it there.