If you want to try option B get a SFC sunroof. They should have sizes that fit the S13.
My car was originally a Non-sunroof car but one of the owners decided they wanted a aftermarket sunroof. Only to find out he loses the glass somehow.
When I purchased the car I could not locate the glass for the life of me so I ordered a SFC sunroof and a shop cut the roof bigger and install the SFC sunroof. The sunroof I have looks to be a bit bigger than that whole area you welded.
I'd have to get the dimensions to see which one I ordered because I cant remember but its a good brand and they sell stuff to repair it if it happens to fail overtime (rubber seals, handles etc)
For the headliner you're going to have to trace the outline of the sunroof by taking the glass off, having one person hold the headliner by hand in the car and someone else tracing the outline of the sunroof from the roof.
Then get a protractor and measure the offset from the inside and retrace your original trace to get a more accurate cut for the inside. Then cut that outside trace and your sunroof should fit.
Hopefully that all made sense