How do I set up my Multi-Site (Etsy-style site) to accept both PayPal and credit cards?

I am trying to set up an Etsy.com style site where I can take a transaction fee from the stores making a sale. I want the buyer to be able to:

1) Purchase products & checkout from multiple stores

2) Be able to use Paypal or Credit Cards

The forums have described that Paypal chained payments need to be used to create a transaction fee. However, they stated that you cannot have both a Paypal payment option and Global Cart enabled. They also stated that you can only checkout from a limited number of stores at once with Paypal. Is this true and is there way around it? How do we solve this issue? Also, what credit card processor options are there that work with Marketpress? I am using the Marketflex theme.

Thanks

Ashish