As a guidance how many levels should an accordion have ?
I have an issue of working on a site that currently does as deep as four levels. resulting in inconsistent interaction styles with each accordion item.
Only one. Nested accordions have an incredible amount of friction and are very difficult to use for people, specially when they're not aware that there are other levels inside the tabs. But even then, expanding/collapsing behaviors will result in users losing track of where they are, what did they click and how to get back to previous steps in the flow. In short, everything will be extremely confusing and annoying.
If you're going to use steps, maybe you should consider to use a stepper, or just plain text with no additional UI. If needed, you can use links and anchors. Very simple and basic, but it works
You can read more about when to use (and when NOT to use) accordions at NNG