If this wasn't possible then I wouldn't be here.

Shit no! A man can get by with sex offender and terrorist. When everyone thinks your a mime though it's hell on Earth.

Sure, but BD still aren't that common, especially on not-so-new computers... A 16 or 32gb usb key is often the most portable solution

Agreed, depending on the size of the GOG library though. I wouldn't backup my nearly 400 game GOG library to USB keys.

Yes. You can even create autorun.inf files to have them launch automatically, and with the newer installers, you can spread the chunks over multiple discs for the larger games.

You can in most cases but I would suggest that you buy external hard drive (pocket size for durability and portability) or large memory stick (I have two 32GB, they're quite cheap these days). Saves you money in long run. If you buy external HDD, you can keep backup of your entire game library and take it with you anywhere.

I generally advise against this, simply because the file integrity checks can be quite cumbersome from an optical drive. I'd personally opt for simply copying a pre-existing raw installation onto a DVD, though that might miss some registry keys and auxiliary programs and doesn't always work.

Backup HDDs or sticks are better for me.

This is certainly the case with the older installers, and I generally tend to skip the integrity check once the game is burnt to CD or DVD, as any integrity issues will automatically be met with a DVD I/O error anyway.

The newer installers make integrity checks optional, which makes installing from CD or DVD a touch easier.