SpencoSpenco Ground Control Shoe Insoles for Women and Men, Low Arch, Women's 5-6 / Men's 4-5

How do I know which arch height I should purchase?

do these have metatarsal support?

I wear a shoe size 8.5 so should i order insoles size 7-8 or 9-10? when i buy boots, i buy size 9 for a little extra room.

Are these made of plastic? How hard are they? How thin? Thank you