A careful reading of US FAR Part 135 would be a good start.
Making contact with HAI in Alexandria, Virginia would be my next stop for information.
Depending upon which developing Country it is....contacting the appropriate US FAA Office holding jurisdiction for that developing country for information and assistance.
Those contacts would be useful even if you were not going to create an air taxi company but were doing a Corporate Operation.
If not an Air Taxi, For hire or charter operation US FAR Part 91 would be sufficient with Part 135 being for an Air Taxi operation.
I know some individuals that might be of some help but do not wish to name them I the public forum.