(a) reject the application if it is insufficient or defective;

(b) make such other and further studies and investigations as he deems necessary to make a finding as to whether the percentage of vacancies in all or any particular class of housing accommodation is five percent or more (such studies and investigations shall include, but not be limited to, data gathered by the United States Bureau of the Census or any public or quasi-public agency, or studies made by independent consultants under contract with the Division of Housing and Community Renewal or by its own staff); investigate the facts presented in the application; conduct such conferences as are necessary; require the filing of such other and additional reports, or other evidence relevant to the proceedings;

(c) suspend determination of application until completion of such studies and investigations as the administrator deems necessary to make a finding as to whether the percentage of vacancies in all or any particular class of housing accommodation is five percent or more. In the event that the administrator so suspends his determination, he shall advise the applicant, in writing, of the reasons for such suspension, including the identification of the studies and investigations deemed necessary by him;

(d) require any person to appear or produce documents, or both, pursuant to a subpoena issued by the administrator;

(e) grant or order a hearing.