1) Weaver's research regarding maternal rat behavior in a key window of time is relevant to humans. In humans, "kangaroo care" or skin-to-skin contact between mother and infant, especially premature infants has been shown to be beneficial for the infants in terms of survival, regulation of vital signs, ease with breastfeeding, pain regulation but also has been shown to have positive effects in social development in young adulthood . (citation: Charpak et al. Twenty year follow up of Kangaroo mother care versus traditional care. Pediatrics Jan 2017)
2) The health behavior outcome I would study is adolescent binge eating behaviors. Previous animal and human studies have looked at the interplay between dopamine pathways and these behaviors. If I were to design my own study I would look at if maternal breastfeeding and duration amount somehow modulated dopamine pathways in the brain and how it may protect or predispose adolescents later in life to binge eating behaviors. The specifics of how I would measure these changes during breastfeeding, I don't know since I am not a basic scientist.
3)I think that Gruenewald's studies are an extension of Weaver findings and not necessarily mutually exclusive. I think that it would be possible that although someone could have a positive influence during early development and may be "programmed" to have a better adaptive stress response, in the face of continued stress loads one could still demonstrate higher biomarkers of allostatic load as Gruenewald shows.
4) I think that Hertzmann and Boyce offer a valid argument and evidence for their "gene-by-environment" interactions. Gene-by-environment effects can definitely contribute to health related disparities especially as you look as social segregation patters by race/ethnicity and SES markers like income it may even lead to an over-emphasis on "genetic distinctions" if you don't take into account that it may only be manifesting because one group lives next to a pesticide farm vs. pacific heights.