Zipper and Interfacing

Hi Everyone! I love how active this blog is-I’m getting so inspired!

I’m making a small tote for my first bag and I’d like to make an inside zippered pocket, which is not included in the pattern. I’m not sure I can figure it out on my own! Does anyone have experience doing this or know of a good tutorial?

Second question: My pattern calls for “interfacing”. When I made my skirt, the pattern was very specific that I needed “lightweight fusible interfacing.” I’m not sure what will be best for my bag: medium, heavyweight, fusible, non-fusible?