Indoor pistol/carbine/BB gun range

I've got a 10m range in my basement currently, but it's basically just a metal rimfire trap on the far end of my garage which I shoot through the doorway from my basement. I'm thinking I'd like to turn it into something better with a backstop about 4' x 4' with spinners and swinging targets.

The guns used will all be low powered, maybe 8 fpe tops, but I'm planning on adding enough plywood backing to stop anything under 40 fpe.

What do you guys think of carpet as a backstop material? Any targets you'd particularly recommend for indoor shooting.