Boxed numbers after an x (i.e. "x1", "x2", or "x4" in a box) indicate the number of times each beat should be played before proceeding to the next beat, as if every beat has a repeat sign around it.
A boxed number applies to every beat until a new boxed number overrides it.
Notes in parentheses should be played the first time a beat is played and omitted on all subsequent repetitions of the beat.
Dynamics: p+ is halfway from p to mp, mp+ is halfway from mp to mf, etc.
Primo:
You are playing throughout the entire piece. To conserve space, the staff is only shown when your notes change.
Accidentals apply until a different accidental overrides it.
Secondo:
In the manual staff, dynamics apply primarily to notes on the upbeat (the RH).
Downbeat LH notes should be omitted when there is a note played in the pedal.
The pedal should follow the dynamics written for the manual unless otherwise notated.