In his report the expert shall make such recommendations and suggestions as to:
(a) The system of accounts kept, or in his judgment to be kept in connection with each public utility.
(b) The classification of the public utilities of the district and the establishment of a system of accounts for each class.
(c) The manner in which such accounts shall be kept.
(d) The forms of accounts, records, and memoranda kept or to be kept, including accounts, records, and memoranda of receipts and expenditures of money, and depreciation and sinking fund accounts, as in his judgment are proper and necessary.