All buildings erected hereafter, all uses of land or buildings established or changed hereafter, and all structural alterations, enlargements, relocations, and restorations of existing buildings occurring thereafter [hereafter] shall be subject to the requirements and regulations of this ordinance, and no land shall be used for and no building shall be erected for or converted to any use other than provided in the regulations prescribed for the district in which it is located, except as hereinafter provided.

Where a building permit for a building or structure has been issued in accordance with law prior to the effective date of this ordinance, and provided that construction is begun within 90 days of such effective date and diligently prosecuted to completion, said building or structure may be completed in accordance with the approved plans on the basis of which the building permit has been issued, and further, upon completion, may be occupied under a certificate of occupancy by the use for which originally designated, subject thereafter to all applicable provisions of this ordinance.