Upload & Sell: Off
Statistically speaking, the more cards you have, the more likely you're going to have a failure.... statistically.
I'm not a fan of the fear of large cards: "all eggs in one basket" I happen to own one house, drive one car, etc... And if you take the extreme of: more cards, less to lose, then we'd all be shooting with 16Mb cards and getting one frame per card.
Yet I understand the worries that most ppl have, and as others have mentioned, I believe you'll get better reliability out of higher end cards. Don't misunderstand me, I buy lots of the smallest (reliable) cards I can find. For my workflow, we only shoot about 500Mb of photos in two minutes and then download each card. So I don't need bigger cards. As for reliability... consistantly, the cheaper cards: from Sandisk Ultra to Kingston, to other (lessor) brands, will cause problems, whereas the better brands: Extreme, Lexar Pro, Transcend, etc... have been troopers during 150,000 images per day shoots, camera/reader swaps and downloads every ~100 frames.
That being said, what size you go with, really should be a matter of your budget and workflow. Bigger cards usually carry a price premium relative to smaller cards. Even if they are a linear price match ($/gb), it's may be hard to spend 4x the amount on a 64Gb card when all one might need is 32Gb.
But if your workflow is better suited for one camera in the card for a whole day shoot, not worrying about carrying extra cards, when to swap, maintaining spent cards, etc.. then a larger card may make sense. Conversely, if you have time and space and a system to manage cards, then saving money may be worth the extra time dealing with multiple cards.