(b) For mortgage payments to be eligible for insurance under the provisions of this chapter, the underlying mortgage shall be one which is made to and held by a mortgagee approved by the authority as responsible and able to service the mortgage properly. Permanent mortgage loans made or insured by the authority under the provisions of this chapter shall: (1) Not exceed (i) ninety per cent of the estimated cost of such proposed housing if owned or to be owned by a profit-making mortgagor or (ii) one hundred per cent of the estimated cost of such proposed housing if owned or to be owned by a housing authority, a municipal developer, a nonprofit corporation or cooperative or by a resident-owner of a structure containing not more than three dwelling units, or of a condominium; (2) have a maturity satisfactory to the authority but in no case longer than fifty years from the date of the issuance of the loan or insurance; (3) contain amortization provisions satisfactory to the authority requiring periodic payments by the mortgagor not in excess of his reasonable ability to pay as determined by the authority; (4) be in such form and contain such terms and provisions with respect to maturity, property insurance, repairs, alterations, payment of taxes and assessments, default reserves, delinquency charges, default remedies, anticipation of maturity, additional and secondary liens, equitable and legal redemption rights and other matters as the authority may prescribe. If a loan made by the authority under this chapter is insured or if the project or any units therein are assisted by any department, agency or instrumentality of the United States or this state, and the terms of the mortgage insurance commitment or regulatory agreement covering such insurance or other assistance are