It does.

Look up sourdough recipes. The bacteria and yeasts will eagerly eat some longer-chain carbs. They aren’t picky. Same goes for commercial supermarket yeasts.

It does. The bread I make is only flour, yeast, water and salt. Toss them together and wait 2 hours you have a risen bread

Starches are just chains of sugar.

You can test for yourself if starches are sugar.

Grab a spoon of oat flakes, no milk no nothing, but em in your mouth and chew and chew. It’s a fair bit of work, but soon you’ll taste the sweetness.