jkittlesen: Perfect, thanks for the quick response.
I'll go buy a few !
Just to make sure you realize, there isn't any kind of restriction how many times and when you download your GOG games. You can do it whenever and as many times as you want, as long as GOG servers are up of course.
This is the norm also for other digital stores, no restrictions on how many times you can download your game. The only exception I remember from the past was Strategy First's store, where there was some restriction (either that you can download the game installers only a few times, or maybe there was a time limit, like 30 days after purchase). And maybe Amazon had a similar restriction for some of their digital goods years ago (but not anymore)?
So, unless you are afraid GOG might go bankrupt in the near future, you can postpone downloading your purchased GOG games until your rig is ready.