@WestlakeArt, I'm very sorry for the late reply and thanks for helping your parents get set up!

• Business Category: You should select the business category that relects the business type. There's more information about why this important here: Choose a Business Type for your Square Account. If needed, this business category can be changed — just give our CS team a call.
• There isn't a way to add a second email addresss to a Square account. You can edit the email address linked to the account at any time from the Account & Settings section your online Square Dashboard.
• If you're interested in promoting your business you can use Square Marketing to post to Facebook. Square Marketing is a paid feature but if you want to take a look there is a 30-day free trial. 
• There is a lot of information about getting started with Square in our Support Center - they might want to start with the Square Get Started Guide, or you can search for threads here in the Seller Community.

Last but not least if you haven't already I'd also recommend that your parents set you up as an Authorized Representative. That way if you need to call our Customer Success team they'll see that you're authorized to discuss information about the account (keep in mind,in some cases the team will need to speak to the Account Owner.)

If you have any other questions please let me know!