I have an idea. BeamNG online launching. It's sort of like ACR at http://www.autoclubrevolution.com/en, and all it is you go on beamng.com/play, then sign in. Then the game launches. I really do like downloading the game, than clicking the pin on my taskbar, but my 128 GB SSD in my laptop is getting full, and this will be fine, only if this launcher will pass most internet filters/ parental controls. BeamNG already does at school, so that is good. Just consider, it is a decent idea.
Multiplayer isn't going to be a feature at first if I am correct. They are going to focus on singleplayer aspect. I'd prefer this to be playable offline, for multiple reasons.
Terrible, and your idea wouldn't even save hard drive space. Most of the core game would still need to be on the computer... Also AFAIK, multiplayer is something they hope to accomplish, but it hasn't even been 100% confirmed as being in the finished product. Unless there has been more info in that area that I haven't seen.