Hi, Great questions!
1. It is better to treat points that go together for the most part and to try to do something useful with your self treatment. However, it is ok too to try some random points (just to see how they feel). Just don’t leave these points in too long and don’t do too many at one time.
2. It is safe to practice on yourself a few times per week as long as you are not leaving the points in too long and not treating too many points at once.
3. In general this is the “rule” to which there will always be exceptions. But, yes, you can think of treating the Yin meridians with the needle going with the flow of the meridian whereas with the Yang meridians we do not emphasize this and often may needle more perpendicular.