I'm confused about the whole part 1, part 2, etc thing. is the save data supposed to be carried over somehow?
part1, part2,... means that the packed file is splitted into 6 parts. You need all, but for unpacking it is enough to click on part1 to unpack all 6 parts at once. If you download here the 0.48 version, you need the update to 0.48->0.49 and the update 0.49->0.50
22 GB are for most servers a problem, if you are not a paying customer. And even if you are, it could create other issues for downloaders or uploaders.
The old save is normally not compatible. I think there are normally old saves included. So if you have done everything till 0.46 for example, you could start from this point with a new save. But I never did that, so don't know the details.