I wanted to do the exact same with my Tumblr blog. Adding a column to the side is dependent on the coding that makes up the theme. Unless you know coding very well, adding one to a re existing theme is not an easy task >.<
As for adding in a whole new page, as far as I have found Tumblr does not allow that. My boyfriend is a programmer, and wrote my whole theme for me. I wanted an “About Me” page but it was not possible. He, instead, had to add in (with code) a floating text box to the site to hold my “About Me” stuff.
If you go to heartofhoney.org and click the “About Me” button at the bottom you can see what I mean ;)
Tumblr is a fantastic site, but is best for single column blogs (Unless you can find a theme with more coded to it). I also looked at Wordpress and they allow multiple pages.
I wish I could help you more :( If you have any questions or need help I’d be happy to ask my SO for you!