What to meditate on?

Hello Dhananjay Sir

How are you Sir
With the help of your grace, its been two months of my brahmacharya practice.
Please help me on my doubts.

1.I am really having problem in meditation, after pranayama,I do meditation in Sidhasana posture,
  A.I am confused regarding what to meditate on, usually I follow swami vivekananda teaching,which is "imagine a lotus above your head, in the centre of lotus is the Almighty, the Intangible surrounded by effulgent light" but I am unable to do it, I am confused regarding what to see, how to see something intangible, so rather I keep concentrating on light and the light keeps moving,I am unable to concentrate on light also, I have seen your answers too, you suggest to meditate on formless supreme but how to meditate on something which is formless, this is exactly my question, how can we imagine which have no form, light also has form, so we should not meditate on it,should I concentrate on the point between my eyebrows, or imagine some deity, I feel I can do it, so my question is, on what should I meditate?

B.After 10-15 minutes of meditation I try to feel my right leg, which is stuck in the middle of the left leg in Sidhasana posture, I try to feel that circulation has stopped there, and I break my meditation unwillingly, padmasana is much more difficult for more me, as soon as I sit in this posture, again I feel my right leg, trying to get out of that position, as circulation stops there.

2.Till today I thought we can tell people about our vow, but reading past answer I knew that we should keep it as a secret.
Till now I have said to only my ex-ggirlfriend about it but along with this after knowing the adverse effects of masturbation, I am nowadays recommending every friend to stop it and telling them that I have stopped and u also must stop, should I stop this or keep telling them?

3.I read one answer, you suggested to perform sadhna facing north or east, so my question is what is the significance of direction in sadhna, is it astrology, do you believe in astrology?

4.Sir, have you had Samadhi during meditation?

THANKS