It's legal. They used to cover pretty much all of it then published came at them one after another to want a "deal". The moment they gain any kind of popularity, they're going to hit the same legal wall.
As for using it for your own needs 1:1, I wish steam would expand it's steam to steam self streaming to cover usage out of local lan.
The initial pairing has to be done on lan I believe, but will work afterwards through Steam. I remember trying it with a Raspberry Pi even. Steam itself will also work as a client and not require the initial pairing setup.
You can use Steam to stream over the internet. You have to enter a pairing code once on the remote machine, but after that you can play anything, you can even add a "non-steam game" to stream any application you want.
I do this all the time with my powerful work computer at the office while I'm at home. It works surprisingly well, actually.
The only shitty part is that they removed the ability for you to download a new game on the remote machine from your local steam client. The only way to do it now is with the steam app on your phone.
As for using it for your own needs 1:1, I wish steam would expand it's steam to steam self streaming to cover usage out of local lan.