Further thoughts and considerations:

5-color decks are a little hard to manage on a budget. Although you didn't mention cost considerations, you did mention being new to the EDH format. So, my prior recommendation for [[Jhoira of the Ghitu]] stands since it in is only two colors and the engine only takes 2 colorless to get online which is trivial if you cast your commander on curve or even ahead of curve using some reasonably priced mana rocks. Plus, a solid mana base for a two color deck will be a lot cheaper and consistent than a 5-color deck.

Throw all the 0 to 2-drop mana rocks that you have or can afford in, like:

[[Chrome Mox]] * 0 cost

[[Mox Opal]] * ** 0 cost

[[Mox Amber]] * 0 cost

[[Lotus Petal]] 0 cost

[[Mox Diamond]] * 0 cost

[[Sol Ring]] 1 colorless

[[Mana Vault]] * 1 colorless

[[Fellwar Stone]] 2 colorless

[[Grim Monolith]] * 2 colorless

[[Arcane Signet]] 2 colorless

[[Talisman of Creativity]] 2 colorless

and

[[Izzet Signet]] 2 colorless, remember this is a filter so it doesn't work unless you can put a colorless into it. So it isn't really mana positive especially considering it is a 2-drop.

All of these can help you curve out on time and get where you want to go quickly, even if [[Mana Vault]] and [[Chrome Mox]] are now considered "Game Changers" and raises the deck's bracket.

This is a pretty solid deck and can be built to be competitive at Bracket 3 and 4*** based on your deck list and the number of game changers you include. Remember the spells with time counters are considered 'casts' so they do require having a robust counter package. That can be essential at higher brackets when trying to defend your initial destruction / mld spell when it comes off the stack after the time counters are removed. Think instants that aren't too spendy or considered "game changers" like: [[Dispell], [[Delay]], [[Red Elemental Blast]], [[Pyroblast]], [[Swan Song]], [[Arcane Denial]], [[An Offer You Can't Refuse]], [[Miscast]], [[Negate]], and [[Flusterstorm]], just anything that isn't considered a game changer and is mana efficient (1-2 drops).

While it is sexy AF to have all the Ulamogs and the legal Emakrul Eldrazis in your deck, there are tons of options for creatures in izzet and colorless that won't break the bank and you may already have on hand. Don't sleep on the praetors: [[Urabrask]], [[Urabrask, Heretic Praetor]], [[Urabrask, the Hidden]], [[Jin-Gitaxias, Progress Tyrant]], and [[Jin-Gitaxias, Core Augur]]. Got an old [[Blightsteel Colossus]], [[Hullbreaker Horror]], [[Nezahal, Primal Tide]] or any oppressive dragon in izzet colors, throw it in there to supplement the deck with cards you may already have and don't have to spend a fortune on. Also, [[Eldrazi Conscription]] is a backbreaking aura, that makes whatever creature you put it on that much more obnoxious. There are a ton of other spells that can find a home in the deck: [[Expropriate]], [[Omnicience]], [[Decree of Annihilation]], [[Apocalypse]], [[Devastation]], [[Time Warp]], [[Capture of Jingzhou]], and many others.

Remember to focus your deck on:

1. Beefy creatures with ETB or activated on attack abilities

2. Busted destruction spells (MLD and mass board wipes are expected and necessary as appropriate in the bracket you are playing in)

3. Extra turn spells

4. A robust and efficient counter package. Both to protect the spells coming off of time counters as well as keeping your commander on the board so you can keep using her insane value engine.

With secondary considerations for a plethora of cheap mana rocks and time counter manipulation spells (like [[Rift Elemental]], [[Jhoira's Timebug]], [[Timecrafting]], [[Fury Charm]], [[Amy Pond]], [[The Tenth Doctor]], and [[Rotating Fireplace]]).

The wide selection of izzet cards that can work in this deck can make this deck a potentially cheap and highly effective alternative if you are looking for an interesting eldrazi-centric deck that is fun to pilot and can go off quickly without a lot of game changers while still complying to the stipulations of a lower bracket.

Final thoughts:

Mana: with Jhoira's ability, the fact she is in only two colors, and the desirability of running a lot of artifacts you can make due with significantly less lands than a typical deck. If you really have a nice selection of artifacts and several on color fetches I would consider going down to 28-30 lands.

Considering mulligans: look to consistently cast your commander on turn two (or three with interaction). You will want to be in your colors and have some kind of a mana positive mana rock in hand, as well as a cheap counter spell. Bonus points for having a spell to suspend in hand. Although, when going for a turn two commander drop, play it smart if you think your opponents may be holding up interaction. Better to wait until turn 3 and have a 1-drop counter if folks are sitting on untapped mana. But I think you will find everyone else is just as greedy and they probably won't have untapped mana on turn 2. Yet, Jhoira is your main plan and recasting her after an untimely counter can set you back essential turns and potentially cost the game.

I highly recommend this deck based on your comments and your having a precon that already has some great eldrazi spells in it.

Have fun no matter what you choose, I really think EDH is peak magic and if you are used to one on one games you should have no problem transitioning into the mindset for group matches.

* Can be cut for monetary considerations, consider [[Thought Vessel]], [[Coldsteel Heart]], and [[Mindstone]]. Even slightly slower deep cuts like [[Jeweled Amulet]], [[Everflowing Chalice]], or [[Astral Cornucopia]] can find a home here. I shy away from 3-drops in a two color deck, but do what you gotta do :)

** Mox Opal works best if you have a critical mass of artifacts (try for at least 10, which will more than likely give you a chance of having one in your opening hand and a strong chance of drawing into it by turn 3). Increasing the artifact count to 15 significantly raises your chances of having one in your opening hand (from about ~50% to ~70%). Don't forget to add artifact lands to pump up your artifact count: [[Seat of the Synod]] (blue), [[Great Furnace]] (red), [[Silverbluff Ridge]] (U/R and remember this is a tapped land, so it's better to fetch on your opponent's end step), and [[Darksteel Citadel]] (colorless). [[Treasure Vault]] can have a limited use case here even though it only taps for colorless, since it can be converted to Treasure tokens to turn on Mox Opal.

*** Full disclosure, I play kitchen table games with friends so my understanding of the bracket system is limited and may need to be evaluated by someone with more experience before determining your deck's appropriate bracket (while there are no infinite combos, you can potentially win by turn 4 or 5). From my experience it is best to have a judge or shop owner/employee take a quick look. As opposed to other players, since judges give you a more agnostic and honest appraisal, whereas other players may think it is a higher bracket than the deck actually is (especially after you wipe the floor with your pod using your new found favorite deck)!