Your scanner investment will last years, so it is recommended to start out with a sophisticated software that is as good as your professional art work.
Textures are the most fun to scan, since many objects fit nicely on a flatbed scanner.
You can use the textures as fill for large lettering for posters. You can use the textures as background for your poster. If you buy stock photo backgrounds, everyone else can tell where you got your designs from. Stock photos are published in every catalog for all the other designers to see. If you use a unique background, that you created yourself, your designs express more of your natural artistic ability.