@mb14_ESO,
I'd guess it will be a 20GB download, which means you should have around 50GB free disk space - for the initial download, and working space for when the patch is applied. (Actual final additional space needed will be much much less).
Caveat: I have not downloaded the new content from PTS, so this is just a SWAG based on comments about the amount of new content, and trying to remember back when update 1.6 was released. Oh yes, and also based on half remembered comments from guildmates who HAVE downloaded the PTS patch.
And yes @DragonSamurai360, those of us with slower internet connections (like my 6Mb) will be offline for 10+ hours while update 2.1.x downloads and installs.