Brahman realization is considered catastrophic in the sense if one does not make further progress to Krishna Consciousness. The less intelligent class of men give more stress on the Brahman realization and they take it as final, so this conclusion is a catastrophe. Because one has to make further progress for Paramatma realization, and further progress for God realization. If one finalizes everything by Brahman realization, certainly that is a catastrophe.
Yes, without cleaning the mind, nobody can advance in spiritual understanding. And the chanting of Hare Krishna is the cleansing process of the mind. That is our motto.
When one realized the Personality of Godhead, he automatically realizes the impersonal Brahman. When you understand what is the sun planet, automatically you understand what is the sunshine. Understanding of the sunshine does not include understanding of the sun planet. So impersonal realization is always imperfect, whereas personal realization is always complete and perfect.
Yes, the point is that we should not eat more than required. Eating, sleeping, mating, all these are material demands; the more we minimize, then that is good, but not at the risk of health. Because we have to work for Krishna, so we must maintain our health nicely. But we should not eat more than is required for maintaining body and soul together. That is the principle. It does not mean, however, that if one's body requires more food for maintaining it, that he should imitate someone who requires less food. The real point is that eating is for maintaining the body, not for luxury or for satisfying the demands of the tongue. Yes, you are right in saying that in the beginning of devotional service that one can only see Krishna in the Deity and the prasadam that is offered to Him. But, anyway, if anyone has the tendency to eat more, then let him eat more prasadam, than any nonsense, but eating more is not encouraged. But it is not that if I want more food that, artificially, I shall eat less. Yes, green dahl, yellow dahl, it does not matter, they are both o.k.