The Certificate of Authority and Sales Tax ID number are issued by the New York State Department of Taxation and Finance.  You can apply by visiting the NY State DTF website.
do we get a surety bond with you?
The DMV does not provide Surety Bonds. You will have to contact a surety insurance company and have them fill out the Dealer Bond Under NY State Vehicle and Traffic Law Section 415.
last question, what does our official registered dealer sign have to be size-wise?