Building a deck around Araumi of the Dead Tide using only commons and uncommons (a requirement for the Artisan format, which my group builds decks around as a secondary format) was pretty simple, albeit still layered with lots of possible wincons: get enough cards in your graveyard to have the right options to work with, get enough access to mana, then use Araumi to encore a creature that can untap Araumi once for each opponent... the more opponents, the more effective Araumi is.  Being able to untap Araumi three or four times and pay for the associated encores can easily win the game with access to the right cards.  Like, if you have three opponents, and during your second main phase you encore Aphetto Alchemist to be able to untap Araumi three times, then untap it and encore Marauding Blight-Priest, then encore Kalastria Healer, and then Zulaport Cutthroat, with each creature making a copy for each of your three opponents, they will lose 54 life from the Maurading Blight-Priests, 18 life from the Kalastria Healers, and 36 life from the Zulaport Cutthroats, all while you gain 54 life in the process... each opponent loses 108 life, and all for 9 mana.  That being said, remove the Blight-Priest and you can still force your opponents to lose 54 life each, and you gain 54, for only 6 mana.  If you have more opponents, they lose even more life each and you gain more life.  This is the way... with this Araumi deck, and there are many cards that can get the job done like this.

Because milling yourself is so crucial, there are more cards that mill than cards that do anything else.  Next is ramp, which is kind of two categories: early game ramp, like your typical mana rocks, then creatures that ramp after Araumi encores them, to be used for more Araumi encores (like Cathodion and Soldevi Adnate).  Because colorless and black mana is primarily generated from cards like Soldevi Adnate, having Norritt in the deck is a must, being the only creature you can encore using black mana that untaps Araumi (all the others require blue, which is harder to generate via creatures Araumi can encore).

After milling and ramp, creatures that untap Araumi are the next key ingredient in the deck, followed by creatures that force life loss, as seen above.  After that, everything else in the deck is there to give it some flexibility and diversity of options.  Stuff like Dusk Mangler makes for a great one-turn use of Araumi, where with three opponents each of them will be discarding three cards, sacrificing three creatures, and losing 12 life.  Not bad for 7 mana.  And it's even better with four or five opponents.

Normally I wouldn't think twice about putting Thought Vessel in a deck, but not having a maximum hand size can kind of hurt you with Araumi, as having more than seven cards is a great way to discard a creature from your hand that you want to encore with Araumi.  Having no maximum hand size makes that much more difficult to accomplish.  Frankly, while I also love lots of card draw, with Araumi I want cards in my graveyard to spend mana on, so milling myself almost replaces card draw... not that I don't want to have the option to draw cards too, there's just less of a need to prioritize it as much as I would in other decks.

It should be noted that Undead Butler tokens disappear when they go to the grave, so they can't be exiled to bring back a creature.  But milling three cards on ETB for 2cc is strong enough that they are warranted in the deck, especially being a Zombie (this deck likes them), and having a small chance to be used late in a game to bring back Laboratory Maniac via being cast from hand and then sacrificed to an outlet... it's a small chance, but it's a secondary benefit nonetheless.

Selhoff Occultist is tempting to put in, because it can mill a lot of cards when it's one of many cards that get encored in the same turn, but it's limited by the fact that this is about the only way to really get solid value out of it.  If you cast it early in a game, you'll probably have to wait a while before four creatures have died (to mill four cards), which is what other 3cc cards can immediately mill you on their ETB.  Granted, being able to encore it with three other encored creatures, equaling 12 token creatures with three opponents, will mill you 36 cards, which is very legit.  But in the best-case scenario that will cost you 6 mana to do (encore Selhoff and three other creatures), and more likely it will cost you 8 or 9 mana instead.  At that point, milling 36 cards might actually be more than you need, or it might be exactly what you need (for Laboratory Maniac).  But because it's a dead draw early in a game, and early-game self-milling is key, it's on the bubble... I'd just rather have cards that will help me mill early in a game, giving me access to more self-milling cards I can encore.  Selhoff Occultist doesn't really help me mill much in either of those scenarios until I am able to untap Araumi multiple times in a turn, have enough of the right creatures in my grave, and have access to enough mana to encore multiple creatures.  So I've chosen to take it out, but putting it back in is entirely understandable.  I may eventually do so myself as well.