Mixing fabrics of different materials

Hi all o/

I'm having some questions about working with silk and cotton. Namely I have a structuring layer made of heavy cotton (coutil) and another one of dupioni silk. But the thing is there should not be any shrinkage as it's for a garment not intended to be washed and I assume the coutil to not stretch on it's own. However, there should be a lot of tension put upon the fabric and the threads.

I was wondering if in this instance I could use polyester threads to sew that project. I know that I'm supposed to use a thread of the same material the fabric is made of but in this case which should it be ? Cotton ? Silk ? And as it should not shrink but being under tension, will it matter ?

Something else that was concerning me was working with silk, being my first time working with it. The threads of the fabric are so small that I'm constantly afraid of breaking them while using pins and needles. Is there some special care/technics I should or should not use while working with it ? I'm only aware of the washing temperature.

That's it for me. Thanks for reading and have a wonderful day !