Took a while but Steam finally decided to take my money. Steam says my download is about 85GB. I wasn't paying real close attention before clicking the "Install" button, but it was much bigger than 66GB. Now for some thumb-twiddling while it downloads.
EDIT: package size settled down to about 60GB, so the extra space was likely for decompression
EDIT 2: two hours to complete the download - Steam's servers are getting hit pretty hard today.
Last edited by TESGuides; 06/10/20 06:54 PM. Reason: additional info