Setting Up Paypal Chained Payments in Marketpress

I've gotten really lost in the process of trying to set up paypal chained payments for an Etsy like site in Marketpress.
I was following instructions here https://premium.wpmudev.org/forums/topic/xcommerce-application-process-marketpress-fundraiser
...and got part way through an application on Paypal developer (stopped to go back and create a terms of service page on my site) and now it seems as though several of the links and illustrations on this insructions page are outdated. Even when I navigate back into Paypal Developer I am unable to locate my partially completed application.
However, at this point I have an API signature, userbame, password, and a single app name for a test account with test credentials and live credentials.
Can you send me to any up to date tutorial that will get me on track - I've kind of lost my way at the moment.
Thanks!