Our survey said....fabric choices

So far I've stuck with cottons and poly cottons, playing it safe. I know I need to branch out and try other fabrics. But...I am terrible at recognizing fabrics, their qualities, sewing difficulty, treatment and what projects they will suit.

My first step I decided was to do a survey, of my wardrobe. Taking particular note of the items I like to wear.

It seems viscose, cotton, and blends of viscose come top, with polyester blends second.

Now I have questions:
viscose...is it always stretchy? Is it nice to sew with? Easy to get hold of?
Why can I wear polyester blends but anything 100% polyester is left unworn?

Oh, and I got some 'vintage' buttons given to me.

Aren't they just asking for duck egg blue fabric & white piping?