Tableau is not Excel. Tableau is not an extension nor an "add-on" of Excel. They are very separate products/applications. Given that...
2. No...but with a caveat: It's technically possible but not what I would consider easy for a typical end user. Look for Tamas Foldi, he's done it or at least experimented in doing it. However, I would NOT recommend having your reporting application make changes to your database, baaaad ju-ju! Not smart.
Starting in Tableau 10.5, you'll be able to use Analytic Solver to export your model from Excel to Tableau, This will require you to have a license to Analytic Solver in order to build the custom extension with your model in it. See www.solver.com/export-tableau for more information.