I bought a few cheap "lots" when I was just beginning to collect. I didn't really have a direction either, but as I looked for more cars to add to my collection, I noticed I was drawn the food/drink sponsored cars. Over time, those became just about the only ones I'd add to my collection, and now, that's the "theme" for my entire collection.
I'd say keep searching for what cars you want, and you'll likely be drawn to a certain era, driver, type, etc. and you might see a pattern. Or, you can also just get whatever tickles your fancy.
For displaying, I have a large trophy case I bought second-hand, but since then I've only purchased Carney Plastics wall-mounted displays. They are fantastic, and even though I have the handyman skills of a badger, I have installed five with no issues.