I'm also working on an atraxa angel tribal. A few things ive found that might help your deck:

Enchantments:Cradle of Vitality will help you throw alot of counters on your angels making them even bigger threats that will only grow bigger with Atraxa.

Angelic Accord since you can gain at least 4 life every time you deal damage with Atraxa you can throw down some mean angel tokens. There is also the better known Luminarch Ascension but that is a huge target. Your running decent protection though so may work for you. My favorite is Entreat the Angels cast it for Its miracle cost and just sweep the board with angels. These are obviously all weak to board wipes which the rest of your deck seems to benefit from so I could see you not including these but I find them great since most angels cost so much mana.

Duelist's Heritage can really help you hit for crazy damage with any of your bigger angels.

Cathars' Crusade I'm sure you have already considered this and I know the deck isnt built around Atraxas proliferate but I feel Angels are just meant to have counters placed on them to truly dominate the skies over dragons and other big creatures. Pair this card with one of the token generators I mentioned above plus Atraxa and you will have some serious threats.

I have found Frontier Siege useful in helping with mana. You also get the option to use your flyers to take out your opponents blockers and other pesky creatures without using up your control cards or risky combat. Its sister card Citadel Siege helps either throw more counters on angels or tap down blockers (or the scary Eldrazi eyeing you across the table).

Removal:I dont know many good ones that arent in white (and you have more than enough cards running white) but I will still recommend a half white card Sylvan Reclamation because of the options to exile stuff or landcylcle. And in 4 colors, you need dem lands.

Recursion:You have most of the best ones so I can only suggest Necromantic Summons since you get more counters to exploit. The high manna cost weighs against it compared to your cheaper options so this is definitely a 50/50.

Card draw:I definitely recommend you get at least 3-5 more card draw cards since that's a big game decider often in EDH. There are too many good ones to list here but I will say Brilliant Spectrum since you have 4 colors (though there are many cards that will let you draw that many cards without discarding that are more expensive) and Tezzeret's Gambit since proliferating is important for those mana rocks and lands with counters on them. Mana is huge in an angel deck. Speaking of which...

Mana Ramp:There are the obvious green ramp spells like Cultivate and Rampant Growth (personally I go with Map the Wastes for that bolster counter) and I recommend any of them if You can since 4 color decks need help with the mana base. Having Astral Cornucopia is a great choice, but you should also swing Everflowing Chalice since it does the same with colorless mana. Mana is really important in a deck with so many high costing creatures, even if your cheating them out alot with reanimation cards. Also lands like Dreadship Reef that can be proliferated. If you have room for it, I find Alchemist's Refuge useful for flashing in big angels as blockers or on my opponents end step so I get to attack with it on my turn without it risking being removed off the board (angels are big targets after all).

Cards to remove: Avacyn, Angel of Hope and Akroma, Angel of Wrath are very good angels, but their very high mana cost combined with them having 3 white in the casting cost really hurts in a 4 color deck. Cards like reanimation do help you cheat them out, but you aren't going to be able to do that often enough to balance it out. If you dont run into a mana problem when you play the deck however then they are fine additions.

Sublime Archangel very good angel but maybe not good in this deck since you may not ever have more than 3 or 4 angels out at once and you will want to be able to attack with all of them.

Sigarda, Host of Herons also a great angel, but since you have so much graveyard recursion, may not be the worst thing to have to sacrifice them. She is amazing still though and only take her out if you have nothing else to take out and you have an even better angel to replace her with.Fractured Identity I like this card a lot but doesnt seem to have anything to do with the deck. Maybe replace it with something like Crackling Counterpart? Then you have 2-3 awesome versions of one of your own angels.

I hope this was helpful. Angels are what got me into commander and are my absolute favorite type of card. Atraxa is perfect for filling in the weak points of an angel deck and is an amazing commander. Flavor is also extremely important to me when I build decks and you have alot of it in yours which is good to see. Atraxa is the single most popular commander in EDH right now and with good reason, but with all the proliferate and infect decks people are making you can swing in out of no where with angels and just wreck people. Now go destroy everyone with the best creature type in the game!