How am I supposed to play the staccato in the following section? I also don't understand when composers write 8th on bottom and then a 16th on top. Why do composers do this?
As I understand it, this is the common approach when writing multiple voices in a single staff, for example with choral music you will have four voices (Soprano, Alto, Tenor, Bass), and each voice follows its own independent rhythmic markings.
In this case, there is a melodic voice (played with fingers 2-5 of the right hand) and the accompanying chords, shared between the 1 finger the right hand (the 8th notes) and the left hand. Notice that they all share the same markings, as they are 8th notes + an 8th note rest, independent of the upper voice. This could work in theory independent of the staccato marking.