No way, don't, never did and never will. One (and infuriatingly, after they gave up on the second specific one, flat pricing, and muddled the less specific ones (goodies, making sure it works...). the only remaining) selling point of GOG was DRM-free, right? Among the requirements for something to be called that is not needing to do or use any other software other than a regular browser to download the game, and none whatsoever to install or run it, and not have anything check for a login or a key or whatever anywhere. No difference between it being "optional" but choosing to run it and it being mandatory, after all, as in either case it'd be running, and "calling home", likely with the login as well, and the point of GOG was to stay well away from any of that stuff.
What do you mean by install one at a time or multiple? Not sure how you'd install more games at the same time (I mean, you could, but system will struggle and it'll be slower than installing one after the other, especially if still on a HDD). As for organizing, as Leroux said above, using those things called desktop shortcuts, my installed games are in a column on the right side of the desktop (other programs in the first one on the left, links to commonly used folders or files in 2nd on left). Also have keyboard shortcuts, for commonly used programs it's ctrl+alt+[first_letter_of_name_or_of_a_word_in_name], for files it's ctrl+alt+[numpad_symbol], for games it's ctrl+alt+[numpad_number], in the order they are on the desktop, top to bottom. And, of course, they all go in D:\Games