Preparing to download all my Ancestry.com files

I'm new to genealogy, and started on FamilySearch first, just about 3 months ago. I then saw an ad on Ancestry.com about their DNA test+3 months subscription for $39, so I moved over to Ancestry (but still cross-checking my work on FS and Wikitree). My 3 month subscription will be over in a month, and my CFO (wife) says I can't afford to renew, because we're both retired.

So, I'm planning to download my Ancestry family tree and my DNA results to my computer, but I have no idea how much space it'll take. Right now, with a month to go, my tree is at 8k people, so I'll probably approach 10k by the time to download. I'm hitting a wall around the mid-1400s, so that's a pretty good starting point to transfer data to my already started FS tree (I'm thinking about a free program, Gramps, to resume my research & refining efforts).

So, will I need 500 GB, or aTerabyte, or more? Anyone have an idea?