I already have a PayPal business account. Do I need a seperate Braintree business account for Braintree integration or can I use PayPal business account itself.
What kind of Braintree integration? For PayPal Checkout via a Braintree SDK you can get credentials at the bottom of: https://www.paypal.com/signin?intent=developer&returnUri=https%3A%2F%2Fdeveloper.paypal.com%2Fdeveloper%2Fapplications . There's some information about this specific integration here, although most of what you need will be on the Braintree site.
If you want other Braintree gateway features, you need to apply for a Braintree account for your business. It'll be connected to your PayPal account.