This sounds like a fun and creative project. I just want to voice my concern about decopauging pictures onto your walls. If you're planning to stay in your house a long time it's probably fine. But if you plan to sell and move in the next 5 years, you will have a monster project scraping that off your walls and it will turn buyers off if you don't remove it. You might have to put new drywall over it, the decoupage could make it impossible to scrape off.
That said, you can find all kinds of images online. Save them to your computer and edit them to b&w if that's your preference. I love the kitschy line drawings of the 50's and 60's, especially that mid-century cocktail party food.
You can find great retro/repro fabrics, it would be cute to make window valances and trim some dishtowels with an old kitchen print.