Adobe Illustrator is the best option because graphics are vectors, meaning you can size and resize your images without making them pixelated. You can create poster sized images or cake toppers with the same graphic and the quality of the graphic won't be affected.
Another handy tool for printable assembly is a score board. You'll use it to make creases in paper for easy and precise folding. Don't feel the need to buy all these items at once. It takes time to acquire all the tools for printables, but in the end, you'll find that the investment will be small for a fun and creative hobby or business in printable design.