PayPal Chained payment setup questions

So I'm setting up Marketpress on a clients website and I will be using PayPal chained payments.

I had a few questions.

1) Is it better that I set up the PayPal/ application? or my client?

2) The website is currently in a local testing environment and wont be made available live until it's complete. The application says to provide both user login information and a walkthrough on how to checkout. How are these provided in my case?

3) Related to the previous question, they're asking for a walkthrough on how to purchase through my site. I don't know this until I'm done setting up the application and getting an API key, correct?


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