Well. These are in fact sort of hard questions to answer.
Technically, you aren't supposed to fly over 400 ft above ground to stay within the AMA Guidelines, which we highly recommend. If you are out in the middle of nowhere, the rule is 1200 ft AGL (above ground level) in order to stay out of the way of aircraft. If you aren't close to an airport, they shouldn't be below that.
There was recently a court ruling that said the FAA doesn't have any jurisdiction in regulating remote control aircraft. The people mentioned in this article do a lot of sketchy stuff and post it online. Personally, I think they were asking to get in trouble...
How far is an interesting question as well. With FPV and a strong enough transmitter, it is possible to operate miles from your location. This falls outside the AMA Guidelines.
With your Vision, it will let you know when you get too far away. Most times, the video will start to drop out and you will need to bring it in a bit. DJI quotes it as 1000m. I have yet to see that.