What information do you need to build the payment gateway of my website?

We need the following information from you for the payment gateway,
1. Name of the Payment gateway
2. Technical documentation/ Integration guide from the payment gateway provider
3. Mobile SDK if any provided by the payment gateway provider
4. Test credentials (for both Merchant account and Customer account)
5. Live credentials for making the gateway to LIVE
6. Any special instructions that we need to follow while making payment or making orders using that payment