Can histamine potentially disrupt normal cell cycle, and in high enough concentration disrupt apoptosis? Is that why stress causes so many problems?

Not clear. Histamine can effect apoptosis of certain types of cells like monocytes or keratinocytes. This does not necessarily indicate that the same effect occurs with other cell types. Histamine is also a neurotransmitter effects the brainstem to cause wakefulness. This is why centrally acting antihistamines cause drowsiness by blocking this effect. These effects may be unrelated to stress.
Not known. I am not aware of any effect of histamine on the cell cycle. Histamine is also not usually associated with stress although there are many other cytokines which are.