Read the Apocalypse Situation in trade a while back, enjoyed it but wanted to catch up the Messiah trilogy before I carried on with the title, which I've done, having trouble finding all the back issues though, could I just pick it back up at #11? Seems like all I'd be missing is Deathlok Nation (which I heard was so so) and some one shots =/ 
 
Thanks

With the exception of the magneto One-shot, all the issues are important. 5-10 seemed like a side track at first, but then in the second half of the Dark Angel Saga, the Dethlok storyline comes into play in a big way, especially regarding Fantomex.

The Magneto one-shot, while not being part of the main story-line is still a good issue. The other one-shot, about The Shadow King, is important as it serves as the kick-off to the Dark Angel Saga.