we do not share your data with anyone and there are many ways to control the visibility and storage life of your data here.
but the internet is a public space and you should always assume your data could be compromised.
be smart with your password, use tor or a vpn, and use pgp for sensitive communications.
Yes, your seller will change the status to "sent" after it is mailed. Remember this isn't UPS automated logistics. The seller is often going to the post office herself and then returning later to mark the shipments as well as tend to other business, sometimes this can add a day or 2 and often it's the case that it is shipped and still not marked so don't worry unless it's been 3 business days or more.