Illustrations, what should I use?

First anytime you use another persons' work rather it be photo, illustration, art or words you must get permission from the owner to use it/them. You could try looking at royalty free images or HIRE an illustrator or photographer to do the work. The decision of style is really up to you maybe get both styles desired and pin them up on the refrigerator for awhile, looking at them everyday can help make such decision. You could actually do a blended style 50's with a hint of modernism.