How to split table of contents across multiple slides with Latex Beamer

This can now be achieved with the following option on all "backup" slides:

\begin{frame}[noframenumbering]{My Title}
\end{frame}

Source

This will cause the final number (e.g. 25/25) to be displayed on such pages.

As always, a matter of taste.

Beamer has different themes you can use, some of which include that navigation bar and some of which don't. The default theme, for example, doesn't include any navigation bar. All the themes available with Beamer are described in the user guide; just pick one that suits your requirements and use it:

\usetheme{default}

for example.

If you want to alter an existing theme to remove the navigation bar, you can try setting

\useoutertheme{default}

and see if that gives you a look you like. If not, you'll probably have to get into some theme-specific manipulations. The information needed to do this is in the user guide I linked to above.