The Streamline site design was provided with Power Store 1, it is not included in power Store 2 however.
The "Customizing your PowerStore site's design" Tutorial is for for Power Store 1 and is in the Archived Documentation section. This is not to say it is not valid information with Power Store 2, but the Streamline site design that is mentioned is no included for Power Store 2.
Yes, The left column can be removed from the template if you like.
I do not see a problem with the menu when visiting he site you provided a link for.