If you aren't going to use that door, then place the bed against that wall and put a nightstand in front of the door. Paint the door and the door trim (on the sides and top) the same color as the walls, so it "disappears".

Don't block the windows with the headboard.

I would do white curtains and add color with the accessories. One wide pillow on the bed for color. Art, a vase on one night table.

Some pillow ideas

Find a rug and that will be a good beginning. Then you can take a color from the rug for the curtains, or just buy white ones. If it’s a guest room, being able to block the sun, put your luggage on a rack to unpack and have a small dresser for your things are all a gift. People need to know there is room for their stuff.

At least one night stand with lamp next to the bed. Outlets for people to charge their phones. If you have a wi-fi password, leave a note with that as well.

A note to Prime Estate Studio: The reason why your posts are constantly being flagged as sp*m is because you always link to your business, Your advice is good, and your posts will stay if you just delete the link. If you want to advertise, just contact Houzz's business office.