You can access it by downloading the app from https://openbazaar.org/

or browse the offers on: https://openbazaar.com/ however you will need the app to sell or purchase goods.

On mobile you can use: https://gethaven.app/

That's true, though I imagine similar to LBRY once there's a lot of demand for it people will build websites that connect to it just like how Odysee.com allows you to browse LBRY.

EDIT: Turns out you can use OpenBazaar via https://openbazaar.com/ too, but only to view the offers

As far as I know yes the public data, such as the price, images etc, is distributed across users using IPFS which is just like torrent.

I suggest tardigrade.io, because you'll get georedundancy this way