Hi Oski;
Welcome to Permies!
So it sounds like you want to build a batch box
rocket mass heater?
Do you know how to make one? Have you been to Peter Bergs website ?
https://batchrocket.eu/en/ Very specific sizes that they are built.
As far as putting glass in for viewing.
It has been done. Finding see thru fire glass is expensive. Finding Large pieces is harder.
Normal glass or even "heat treated" Pyrex style can not take the temperature extremes.
Heat loss is high thru glass so your batch will struggle to reach high temp.
But the view is spectacular!