The Sith are not a real presence in this edit, so explaining them can come later in the trilogy. They might get mentioned, though.
The Separatists want Naboo because it is the home world of the Supreme Chancellor, making it the most influential political power in the Senate. They were hoping to have the Queen’s cooperation in order to use her to rally up more systems to their cause. There will be an exposition dump scene where the Nemoidians (Re-dubbed and subtitled) will discuss specifics and perhaps talk to a mercenary named Maul via hologram. This would sort of take the place of the conference scene in A New Hope.
Qui Gon will explain the force to Anakin, therefore explaining it to the audience.
Palpatine is the leader of the Republic, that’s all we need to know in this movie because he has a very minor role, only creating the Army.
The Republic isn’t dying just yet, it’s just becoming more corrupt. To help visually show this, Republic ships will be a cold Imperial Gray.
Thank you for the help!