As a fellow enjoyer of Grass Looking Greener (mostly Lightsworn but also some Zombie/Vampires, PK+Paleos, and Skull Servants), I do think the idea is interesting. You're always going to be in a bit of a battle between thematic consistency and power level. For instance, a grave-counting creature like Wight of Precinct Six or Nighthowler would fit the idea of King growing with more guys in the yard, but they would also be disappointingly weak right now since you don't have a lot of mass self-mill at the moment (Stitcher's Supplier and Overlord of the Balemurk are the first things that comes to my mind). On the subject of getting what you want in the GY, it probably is best to have a few more ways of getting specific targets buried at least. With Entomb off the table in modern, I could see Unmarked Grave being the best cheap option instead of or in addition to Buried Alive. This only negatively affects Maha who I already think is worse than reanimator staples like Archon of Cruelty or Sire Of Insanity. Fewer legendaries also makes Persist a great choice. There's also Lively Dirge if you want to stick to the low mana value plan and can afford to pay more mana. Finally, I'm partial to Burning-Rune Demon as a way to extend into more reanimations while being a reasonable threat in its own right. I think it would be cool to run more skeletons for the theme too, although most aren't that helpful. Cards like Reassembling Skeleton or Persistent Specimen could be sac fodder to a Victimize or Hell's Caretaker. Another one that I know can be good in black reanimator is Emperor of Bones, although he has some unfortunate anti-synergy with other cards in the deck like Twilight Diviner. Death Baron is always an option if you find the Corpses of the Lost backup plan doesn't have enough oomph.

Some final notes: It may be more consistent to focus on just the Xu-Ifit negated reanimations. That would involve going up to 4 Death's Shadow and adding in some similar options like Moonshadow or Yargle and Multani. The EDHRec page for Varolz, the Scar-Striped could be a place to start. That all said, having the more powerful effects of non-negated creatures may still be worth the inconsistency of the two plans not always meshing whan you need them to. You do want to have the best options available in either case though. My first cut suggestions would be Gloom Sower, Avatar of Woe, Inkwell Leviathan, and lastly Maha, Its Feathers Night. Finally, I second cutting some lands and would suggest Bitter Triumph as a replacement for Cast Down that comes with a Cabal Therapy option built-in.