Try mocking-up the computer in a small area......SEE what you can work into the window-sill........Tape off an area on the kitchen table........Custom design around the space available
Is this the ground floor where people can see the window ?.....use shutters/curtains/posters........
Maybe start with a slightly deeper shelf / desktop.......Oak/Birch veneer plywood.......trim the front edge with a solid wood edge for looks and comfort............
I'm righthanded.....so starting on the LEFT:
Add a short "box" / platform under the monitor to house the keyboard when not in use........leave a little extra room at the rear to hide some of the extra computer cables and Surge protector/power strip.............
In the center .........Build a little "organizer" pigeonhole for your paper under the printer/3-in-one...........Maybe include a little compartment/box/drawer to hide the "Misc Pens"
At the far right 'park' the upright CPU..........It's deep so that will leave just a little room for the cables and ventilation behind the computer........
Need more room?........add a shelf from wall to wall above the equipment supported by "legs" to provide a bookshelf....storage.......