(1) It shall rent to a tenant dwelling accommodations consisting of the least number of rooms which it deems necessary to provide safe and sanitary accommodations to the proposed occupants thereof without overcrowding, in accordance with a rent schedule approved by the department. Such rent schedule shall be arranged so as to be sufficient, in the opinion of the department, to pay all of the costs of maintaining and operating the project, including a reasonable allowance for depreciation, and may, in the discretion of the department, be sufficient so as also to include each year an allowance for the amortization of all or part of the cost of acquiring and constructing the project not otherwise provided for by grants or otherwise.