1. Apparently the Kree weren't engineered by the Celestials (unless next issue tells us different). The Kree are engineered by a race called the Progenitors. My problem with that is that of course the Kree were engineered the Celestials...they had Kree Eternals. (that said they never have gotten around to telling us about the Kree Deviants)
2. Apparently the Progenitors used a substance called Primagen (Prima Materia) to mutate the Kree. The Kree later used various imperfect variants of that (Terrigen, Amphogen, Antigen, Isogen, Exogen etc) to mutate other races like humans, Kymellians, Dire Wraiths, Centurians and Badoon etc
3. 5000 years from the Last Inhuman guy (Black Bolt? Ahura?) and Noh-Var are talking about the Progenitors coming back
4. Ronan was a real bitch this issue. Man up buttercup you're supposed to be tough bro not whining about your ex-wife Crystal. That said he's hardly the first guy whose life she's wrecked.
Unless I read it wrong, one of the earlier issues established that the future Inhuman is Maximus. He's actually not crazy, but he can see his entire life throughout time, from beginning to end (like Dr. Manhattan). As a result, he seems insane because he deliberately behaves a certain way to influence events.
As for the Kree Eternals, I guess we could simply say the Celestials only experimented on a handful of Kree after the Progenitors, thus creating the Eternals. They left the rest of the Kree as they are and didn't mess around with them like they did humanity in order to create the mutant gene.