*Possible spoiler for those who have not read the manga or seen the anime series*
MFauli: Since Puk is apart of the intro there is a chance that they will not cut him out particularly. However it does seem like the movies are paced only to fill the anime series and maybe a small small part of the events after the Eclipse that in which case we won't see Puk. But the overall feel is that unlike the anime series where the deliberatly cut out Puk and other "supernatural" parts the movies are more true in at least that sense. What I would like to see is how they handle the prison escape and the parts leading up to the ecplise since those parts in the manga and the anime differed quite a bit.
kyubisrage: The anime assassination was Guts climbing roof tops and entering Julius castle. So except for a few changes in the style leading up to the event, the assassination is almost exactly the same. Killing Adon and Julius happened in the same way, and the poison bolt that instigated the assassination plan as well.
Maybe you could try re-reading the manga from the start? A lot of people don't read the anime parts of the manga because they think it's just a waste of time. That however is a big mistake since a lot of parts have been taken out. One thing I liked about the movie was that they actually showed how Guts was raped, something that was cut from the anime series. Even though he dreams about it in the anime, it's too vauge to actually connect those dots, the movie made that part much more clear.