Hey man, great list. I love
the Scarab God. Personally my favourite commander. Thought I'd share my own experiences with you in case they help.
I find that
the Scarab God is better suited to a slightly more control build. Zombie tribal is definitely the way to run him in EDH, but he can make his own horde and is massively rewarded by making the game go on longer.
40 Zombies is a lot. Personally, I run about 30 or so and leave a little more room open for other things. I feel that one of
the Scarab God's biggest benefits is his eteranlize-like ability. It can target any graveyard and can be activated at instant speed. In my experience, when I focus on this, the upkeep trigger just gets bigger each turn naturally, so I dedicate more cards to filling up graveyards and removing creatures. For me it is what sets
the Scarab God apart as a Zombie tribal commander.
Personally, I also run a couple of creatures that aren't zombies. I play pretty casually so these might not be suitable for you, but I have a lot of success with
Fleet Swallower and
Omnispell Adept. The
fleet swallower naturally just fills up a graveyard and gives you so much ammo to "eternalize", and the
omnispell adept let's you cast sorceries at instant speed and for a specific cost. Casting
Army of the Damned for 2U in response to
the Scarab God's upkeep trigger feels great. And if you "eternalize" these two, you can do it just before your turn starts so they are much less likely to get removed before they can do their thing.
With that in mind,
Final Parting is pretty great in this deck. One card in hand and on in the yard feels made for
the Scarab God. I almost always get
Army of the Damned in hand and
Omnispell adept in the yard for that combo, but it's pretty versatile even if a little expensive at 5 cmc.
But generally I think
the Scarab God takes care of his own horde if you want to play it that way. Focusing on big mana to activate his ability as many times as possible, milling and removal so you've got worthy targets and a bit of counter magic to protect from wipes is my personal preferred way to play him. When I play him this way, I find I don't care as much about card draw. It's still necessary, but every creature in any yard is also basically in your hand. And once he get's going, the scry effect means you get to pick the best card out of your top 3, 5, 10, 20, whatever.
A couple of specific cards that I feel have potential in Scarab God are:
Paradox Haze - double upkeep is just insane with him. You could also look for extra turn cards for the same kind of effect. This is pretty great regardless of what archetype you wish to play with Scarab God.
Ulamog's Nullifier - I played this guy on a whim just to try him out and he was gas. The big thing with Scarab God is when he eternalizes, he exiles the creature and makes a copy. This guy lets you put the best things back into the yard to eternalize again, while also countering a spell and is a
flash flyer, so can chump block out of nowhere.
Training Grounds - this thing starts to get a little pricey, but that effect is super strong if you go the eternalize route.
Having said all that, it might be that going the more control, eternalize focused route just doesn't appeal to you, which is cool. If that is the case, it might still be worth just cutting a few creatures for counter spells if board wipes are prevalent.
Hope some of this has given you food for thought. Happy brewing!