There are at least 3 different Invoices starter solution, one was released with FileMaker 11, one with version 12 and a third one with version 13. So it helps to identify the version of FileMaker that you are using when you ask about a "starter solution" file. From the screen shot, I can tell that you are using Filemaker 13.
1) That should happen automatically with no need to change the design of the database. Just be sure that you have entered a price for the selected Product in the products table.
2) Like the Price, this is a check box that you can click for each product record you create in the products table.
For both 1) and 2), you can add new products and specify the price and whether the item is taxable on the Product Details layout.