You always need to stop and or at least slow down first at any intersection, this is just what is called the rules of the road.

You have to stop even if there is no stop line; all you need is a stop sign. To be safe, you ALWAYS stop before turning anyways. As a general rule, if you pull up to a stop at the same time as someone else, the person going straight, or to your right has the right of way. Did the driver have a handicap plate or mirror hanger? If so, the driver had every right to park in the handicap spot.
I’m sorry, I have no website for you; this is just common knowledge acquired in drivers education.