I'm not sure what size games you'll be playing, but I think the librarian is a little much for games below 750 or 1,000. For the same amount of points, you could take a reclusiarch with a jump pack, which would go along nicely with your assault marines.
What weapons do the scouts have? What kind of role do you envision for them? Right now, it looks like they're there to take up the two troops slots in the FOC.
I know you gave your assault marines melta bombs, but I think you're going to want to look into some dedicated anti-vehicular firepower. Skimmers and fast vehicles will probably be pretty hard to catch even with an assault squad, and you can bet more marine opponents than not will have at least one LST in these lower point games.