Nighthowler seems wasted as you'll most likely have next to no cards in your graveyard. Perhaps Kheru Lich Lord might be more useful?

Between Commune with the Gods , Satyr Wayfinder , Nyx Weaver and Sidisi, Brood Tyrant , I've got 15 cards that fill my graveyard. 7 of those are continuous, and the other 8 only cost 2 mana. I've generally not had any problems filling up my yard.

Personally I think Whip of Erebos is just better than Kheru Lich Lord , even if only because whip allows you to choose what you want to bring back. Necropolis Fiend and Sagu Mauler also already have some of the abilities the lich lord gives, lowering its usefulness even more.

That's my reasoning for choosing the way I did anyway, but maybe there's something I overlooked?

The temples are really good to help set up a creature for Sidisi but you don't want a lot of lands entering tapped so the pain lands are your best friends, maybe even mana confluence in there. Ever thought of running Courser of Kruphix to also help pull the lands from your deck so your more likely to hit a creature

You're absolutely correct on the scry- and painlands, and I can't believe i forgot to put mana confluence in there, since i'm actually running it in the paper version of this deck (whoops).

I've seriously considered courser for a good while aswel, but i can't think of anything I want to replace with it. Any of my self-mill options seem better to me as they can trigger sidisi themselves, and the courser fits awkwardly in any of the other spots.

For now i'll try and run two pain- and scrylands for every colour combination,and see how that works out.

I run coursers in my but im also have Nissa in the deck so i can turn the extra lands into creatures. Check it out Sultai, the walking dead i built it for fun cause im going more modern but wanted something to play.