Yeah, definitely get From Ashes, Javik lends an important point of view on events. And Leviathan is almost certainly worth the 10 bucks. And the extended ending is free, so why not? It should only land you at $20. From what I have read Omega is basically a throw away DLC that adds very little in the way of story and the two characters you get to work with are both temporary and only interact with one another. I'm going to skip it... which will be the first piece of DLC in the series that I haven't purchased. That alone should speak volumes.