Re: Billing order.
In terms of poster credits:
Considering how secretive and mysterious Singer has been with Paquin she may be featured on the poster quite a bit. Their tight lip about her role seems to be creative buzz on purpose so I see her being featured on the poster quite a bit.
Lawrence will have a big inclusion on the poster as will Fassbender and Dinklage.
The graphic designers and art directors at FOX tend to work with the younger cast member images and love working with Halle Berry's images so they may give her a bigger photospot than Lawrence on the poster. I just wouldn't count Berry out when it comes to poster placement. She could wind up just as big as Jackman on the poster. They also tend to love Paquin on the posters as well so she could wind up on it but definitely not expecting her to have equal presence as Berry or Lawrence. Ellen Page will have minimal presence along with Stewart and McKellen who tend to have very little presence on the posters.