Unfortunately, as we are not canon familiar, this explanation about Gold Roger and such things is a bit confusing for us. As this is getting beyond the scope of the Society and Culture page, we'd like to ask you to bring this to PM so we can personally address your needs, and so you can elaborate on what you mean. Why don't we focus on your particular situation and your friend's for now? If you can tell us what background circumstances you need, we can tell you how we think it could best fit into the AU.

Again, though, we really cannot create a new region at the request of an individual, especially if you require an entire off screen world with deserts/volcanoes/ice worlds dotting the landscape. With many of your concerns, we would suggest that instead of attempting to AU your entire canon background into the setting directly, you try to AU the spirit of it instead. We believe it is possible to successively AU a character without needing to transpose their personal setting into the AU; there have been One Piece characters in the game before.