Starting off with thumbdrives would be fine. You could always copy them over to a hard drive later.
I would still recommend going with two, one for storage of everything, the second for a complete backup of the first one.
And I would go with 64GB while things are cheap. You can pick up 2 for $20 on Amazon: https://www.amazon.com/PNY-Attache-Flash-Drive-P-FD64GATT03-GE/dp/B0063GKG6I/ref=sr_1_1?s=pc&ie=UTF8&qid=1480436516&sr=1-1&keywords=pny+flash+drive I trust PNY.