Pixelmon Mod

Sooo... I'd like to make some GUI resource packs, to give people more options :) but I don't know how to set things up. The graphics side of it is something I can do, but what are the specifics I need to know?

1. What size/pixel-count/shape do the GUI menus have to be?
2. If I opened a new image in my graphics software to make the images, does it matter where on the screen I decide to place the menus?
3. Do I have to follow the same logic and menu style as the current GUIs?
4. How do I turn it into a resource pack once the pictures are done?

Would really love some advice for this! My first one would be based on the battle menu in Sun and Moon, to make things seem a little more dynamic!

1. You can find all of the Pixelmon assets inside the Pixelmon jar by extracting/unarchiving it. You will also find the file path structure that you will need to match in the resource pack.
2. Positioning must be exactly the same as the original images.
3. It depends on what you mean by "style". For example, you can change how a button looks, but you cannot move the button to a different location or else you won't be able to click on it.
4. http://minecraft.gamepedia.com/Resource_pack

Thanks for the fast reply. Is there a way that in the future, different positions of buttons could be possible?

Changing button locations requires code changes, which resource packs cannot do.

In that case, a mod could change it, right? Though it would be a little strange to make a whole mod just to change the GUI, it could work.

Yes a mod could do it and if you or someone else were interested to do so I'd happily make it so the gui could be easily interchanged