Bad wizard navigation?

I'm working on an installation guide, or "wizard", for a web application. The installation guide will be quite complex, with many different steps, each taking up around a minute or two for the average user to complete.

We want to have the navigation of the guide on the left, as shown in the picture. This allows us for more flexibility as opposed to having the more traditional "navigation bar" at the top, as we can use the vertical space to display clear sub-steps that we can collapse/expand. It's also easier to add steps in the future, if needed.

One possible drawback that I've identified is the rather awkward positioning of the buttons. Most steps will require mouse and/or keyboard interaction in the "content area" of each step. Once complete with a step, the user would have to interact with the navigation menu which is on the left. I am more used to and it feels more intuitive to associate left with "back" and right with "next". We read from the top-left and move to the bottom-right, right?

Am I overthinking this or is this indeed problematic? Can the navigation here be improved in any way?

PS: The user can "skip" steps and hop back and forth as well.