Welcome to the best format imo. I've got a couple of tips for additions and cuts.

To start out, you'll want the new Kethis, the Hidden Hand . Great abilities for your deck. In commander, you also typically want board wipes, and the best one for this deck is Urza's Ruinous Blast . Primevals' Glorious Rebirth will help you get your grave back. Lastly, to help with your colors: Kodama's Reach , Cultivate , Rampant Growth , and Farseek will all help you out, as could Birds of Paradise .

Now for what I'd cut. Untaidake, the Cloud Keeper isn't as useful as it looks, just cause you're going to want to be sure you have all your colors. Time of Need is less useful than you'd think in this deck, because your commander searches legends, as does Captain Sisay . Combat tricks aren't usually helpful in commander unless you're running infect, so I'd cut Blessing of Belzenlok . Iwamori of the Open Fist will probably end up helping your opponents more than you. Eiganjo Castle is arguably worse than a plains, since it can't be fetched by cards like Cultivate , and preventing 2 damage won't matter that often. Sword of the Chosen just doesn't feel worth it to me. And I get why you're running Maelstrom Archangel , but it's not legendary so I wouldn't really bother.

Cheers for the advice LadyZ! I'll make those changes for the deck. I'm still unsure what lands I could further add to the deck (I was thinking maybe putting in a few shock lands). Thank you!

shock lands are great. if you have the money, I'd recommend the bond lands ( Sea of Clouds , Luxury Suite , ect). They're great in multiplayer, which is how commander's meant to be played.

Your deck could probably survive cutting a couple mana rocks if you want to try and squeeze a couple more fun legends in, especially Worn Powerstone and Thran Dynamo . You could probably get away with cutting a signet too.

Some cards I feel you're missing out on by not having are Shalai, Voice of Plenty , as she's a great way to defend your creatures, Dosan the Falling Leaf due to his ability to shut down instants and Vedalken Orrery , and Illusionist's Bracers because of it's ability to double the number of searches you get off of your commander