Hi David - thanks for loop back and here is hoping your todo lists hits 110% in said depts :>) ... seriously, i'm not sure how to loop into WP DB at sub site on network level either but share some data points i think i read along the way as fyi in hopes they might help ...
a) using sub-site RSS into primary site = bad given extra load on server ... not sure about iframes but recall reading something about using switch_to_blog() as best method to get sub-site info from one site to other on network ..??..
b) reading this Smashing Mag article ->
which has link to slideshare by Otto and Nacin ->
and i believe in slide 23 -> 27 there are clues to multisite success ..??..
accordingly, best of ongoing success and to be continued ... cordially, chuck scott