Cracks in window sills normal?

No, door frames are always installed after the interior plaster. Frames at most, if installed flush. You can see this well in practice when you go to existing buildings and notice that there is always plaster under the frame. If you install before the plaster, you are also installing before the screed. Thus, you can practically not install the door frame, as it is set with a minimal gap to the screed and the floor covering.

:) And now everyone reading here knows that you are planning an EIGHT meter long natural stone slab in the kitchen. ;)

We are talking about the front door here. And it is installed before plaster and screed. Different for the room doors.

We are talking here about the front door. And it is installed before plaster and screed. Different from the interior doors.

No, usually not. Plaster + screed leave some space. Door only at the very end and it is slightly reworked.

Twice the work means 2x travel costs and total costs.