http://support.jp.square-enix.com/faqarticle.php?kid=67225&id=5382&la=1

■ Windows only: To play three characters simultaneously
- A Square Enix account
- A copy of the Windows version
- Three registration codes obtained from the product or the "FINAL FANTASY XIV Service Center"
*You can register up to eight registration codes per Square Enix account.
*The "FINAL FANTASY XIV Service Center" website will be available after the game is launched. Please note that the website can only be accessed by those who purchased FINAL FANTASY XIV and registered a service account.

■ Windows + PlayStation 3: To play a character from each a version simultaneously
- A Square Enix account
- A copy of the Windows version
- A copy of the PlayStation 3 version
*You can register up to eight registration codes per Square Enix account.
*Please create separate service accounts for the Windows version and the PlayStation 3 version of FINAL FANTASY XIV. You will not be able to play at the same time if you register the codes under the same service account.
First, let me see if I understood correctly.
The registration code is the licence code for the game.
You can bind up to 8 licences to your SE account.
You can run characters from the same account under different licenses simultaneously.

Okay, if all that is correct, here are my questions:

I think I have somewhere an unused buddy pass.
1 - If I understood correctly, I'm able to register it under my already existent account and log in with 1 character from it, and 1 from the other. Is this correct?
2 - Will I have to pay for two subscriptions, or does the monthly fee account for both?
3- If I have to pay for both, is there any sort of discount for having them in the same SE account?
4- Is it possible to pay for each with a different payment method?
5- If I register this buddy pass in my account, would this give access to whoever logs into it to my account settings and my final fantasy xiv character?

Thing is I already had one buddy pass, gave it away to a friend, and he quit and forgot all his access info. I was thinking of linking this second pass I think I might have available to my account as to avoid this happening again.