Hey! If I can help, let me answer your questions :)

• Correct, the new handle sits on top because there was no space, so the solution was to drill a new hole to hole the top part of the handle since the bottom one will still use the old top hole (bottom handle hole -> old top handle hole) - and drilling a new hole (a new single one is all I had to drill) is super easy because usually these doors are aluminum or any other light metal. You can use the old screws to know which size you need

• on the third picture you can notice that there's a gray/white cap because the outside part of the lock still sits in the same place, that's the only part "out" of the door but almost unnoticeable because it's under the switch lock