To know what size tub and hides you need, you'll need to get the weight (which I know you've already asked the seller for). Generally people use a 6q for hatchlings, a 15q for juveniles, and then a 32q for adult males and a 41q for adult females or very large adult males. These are the sizes found in some racks, such as AP's racks (which is what I have), but anything around that size would work.
I think the small reptile basics hides are the right size for 6 quart tubs, but don't quote me on that since I've never bought one. The only hides I've bought were large hides for my two largest snakes, but since they live in a rack now I don't use hides anymore.