Well most of the achievements are fairly easy. The hard ones are
Collector's Edition,
Gallery Lover, Hidden Pages, I Will Survive, & Pathfinder.
As far as time goes, it I remember I spent about 10hours to get 750GS
I have not the ones I mentioned above. I used the controller for story as it was easier
than the gun, but used the gun for the galleries I have done so far as the gun is easier for them.
Hope this help, I have not finished the game because I can't find all collectibles and waiting a really good guide hopefully.