Can you sell your knitted crafts in a business like on a mannequin

Yes, you should be able to.
You can do that with career outfits you unlock, you should be able to do the same with knitted stuff.

Yes, it's certainly possible. I made a shop that sells books and knits and I was able to dress the mannequin and set the outfit for sale.

Too bad you can’t sell single clothing objects, like hats or sweaters. The mannequin has to be fully dressed or your customers will get weird looks. :lol: