How does Paypal Express work?

I am a user of Google checkout and Checkout by Amazon. I been using paypal by creating a button to request an invoice which I send manually through my paypal. But I am now looking to expand on this and install paypal express as my member site has a lot of international customers and it would be easier to allow them to checkout without waiting for a manual invoice.

My questions stems from the way GCO and CBA work which I LIKE very much in that I can setup them to not communicate orders or any information with my zencart store.

Does paypal have this option as well? I been reading alot of posts and at times it seems that paypal is updating orders in the admin. This I do NOT want. Anybody who uses GCO and CBA can tell me if PP Express also works the same way?

I ask this because I also seen that the tutorial says that the customer will go to there paypal and pick their payment method and shipping details AND then go back to the zencart site to finalize the order. Is it possible to have the paypal screen process and complete the order then send the customer to my custom paypal_checkout_success page screen? Sort of what I got GCO and CBA to do.

NOTE: I know my custom checkout success for paypal does not pull info without talking to paypal, but this is not a problem as I do not use zen cart order ids. or other info stored.

To add to my post above, to disable orders or customer accounts being created in my store admin, would I not configure the IPN settings? And what about cURL, would I also not need this if I do not want updates to my store admin. Just trying to figure this out as if paypal creates customer accounts in my admin, this is a bad thing as I only allow certain customers to register and will mess my database and seqencing of customer id's.

The PayPal integration in Zen Cart is exactly that: INTEGRATED. That means it's integrated into the customer system and the order system. It is NOT merely an addon like your other payment systems which create multiple places for your business to have to manage all their orders and customers. Zen Cart is not just a bolt-on thing. Yet that seems to be how you're using it, and how you're asking people to show you how to reprogram it into being.

So, you have me puzzled.

What EXACTLY are you using Zen Cart for? From the things you've posted here and in your many other threads, you've HEAVILY modified the software to to VERY different things, and here you're saying that you're not even using the customer database or order database nor the payment processing features in Zen Cart. So ... what's the point? If it's just a glorified catalog of things one could select to buy and the order handling happens in numerous other stores, why use Zen Cart at all?