4 Panel Shaker Smooth Door - is this the door which you currently have -
simple 2 panel interior door. with a modern styled home I think either a 2 panel door or a flush door looks best, though in a pinch there are some great 5 - 6 panel doors that could work as well. but for me it's always best to keep it simple.
Divide rooms with french pocket doors. Like the transom Windows above the doors too.
L i v i n g R o o m
David Cobb Craig: Art Deco Doors in N.Y.C. Great blog with wonderful examples of Art Deco doors
This in the corner of the kitchen as a pantry?
drywall to baseboard transition along with door jamb
PAINT all the interior doors this lighter calmer sophisticated gray... benjamin moore rockport gray door
Please paint your front door a welcoming, pretty color: Door in Farrow & Ball's Brinjal, Exterior Eggshell
shadow gap modern skirting board (doesn't have to go around the door, could just end at the door frame)
Making Frame and Panel Doors - Cabinet Door Construction Techniques | WoodArchivist.com