Seeking career advice in cell phone eDiscovery

I would appreciate some career advice.

I am a recently retired IT person, including IT security, who just got his PI license to do subcontract work for two PI friends. One friend is convinced there is a local market for eDiscovery from cell phones, and this market provides an opportunity to make far more per hour than what my current subcontract work pays. If I pursue this, my goal would be to gain enough qualifications to work 10-20 hours per week in eDiscovery work. With my pension and working wife, income is not critical; I am not looking for full time work. I would want to pass off to better qualified people cases where I would get in over my head.

Assuming such a market exists, my two specific questions are
1. What tool(s) would you recommend I master? For example the more I study XRY the more it seems useful for cell phone forensics, which is more than I want to do. Also while reviewing a real life eDiscovery the person needed a different tool from Cellebrite to get the password for an iPhone.
2. How much additional expertise do I need? For example, I assume becoming certified in Cellebrite would not teach me how to make sure Cellebrite did not alter the contents of a cell phone, especially files last modified time/date. In short, I need to know what I do not know.

I came out of retirement last year to do IT work on forest fires. I learned intermittent high paying IT work is great; it’s not the grind full time work is. This year I am hesitant to do IT work on forest fires again since my routine IT skills are eroding.

Thanks for any help you can give me.