Your first question about the jiva's form with particular reference to Bhagavad-gita 8/18 purport "during the nighttime they have no form.'' "During the nightime they have no form'' means there is no material form. The simple understanding is as we are transmigrating from one material form to another, so actually in this material world we have no fixed form. Similarly when we are spiritually perfect we develop the spiritual form to live eternally in the spiritual world.
Letter to Gurudasa, 16 May, 1970