otto theme, do i have to pay more for required plug-ins?

I am quite disappointed. I just purchase the WordPress Theme OTTO, and it looks like I have to buy an extra plug-in Visual Composer to make it work.
Am I right?

Based on the item description for that theme, a fully working version of Visual Composer should be included with the theme via extended license, so there is no need to purchase it yourself (unless you want direct access to VC updates and support).

Please consult the theme manual (or author support), which should explain where to find the installation file for VC and how to install it.