Let's approach this analytically. The best colour for infect is black so regardless of what happens you need black in your arsenal. Other really powerful cards include
Corrupted Conscience,
Triumph of the Hordes and
Blighted Agent. It wouldn't be a bad idea to have both blue and green in the mix, too. Green can offer some powerful ramp and blue has counterspells which means you'll just automatically win. Maybe we cut the infect idea and just use
Uro, Titan of Nature's Wrath and ramp to oblivion...
Wait I got sidetracked. So black, blue and green. Atraxa sounds like the logical choice.
So how do we win? I think a mixture of strategies would offer you the most flexibility. I would go both tall and wide. Lots of small creatures with infect and a few ones (like
Blightsteel Colossus and
Blighted Agent + combat tricks like
Howl from Beyond) that can win the game on their own. That would actually make it a very interesting deck I've not seen before: combat tricks and pump spells in EDH. Green and black can offer you the necessary voltron-y stuff you need at instant speed, blue has counterspells so you just automatically win. This supports the idea of Atraxa. I have no idea what you'll do with white because it's just not very relevant for anything. Maybe it gives indestructible or pro colour for that damage.
Speaking of, protection. You should run all the swords. Hey! White can find you the correct sword for each situation. Not only the swords pump your creatures, make them unblockable but also provide additional value in all forms of Magic. Blue can also find artifacts so this supports my thesis that with blue you'll just automatically win. Blue and green also have recursion so you can get your lost swords and pump spells back. Maybe we should just go full land ramp with Tatyova and maybe
scrap the idea of infect?
Conclusion: you need small dorks with infect that are annoying to block but dangerous to let through. You want lots of combat tricks to give your creatures evasion and pump them to alpha strike people. You'll want some basic equipment to give evasion and pump the creatures. Atraxa can help you proliferate your damage should you not quite finish someone off.
EDIT:
Sigil of Distinction,
Colossus Hammer,
Colossification,
Rogue's Passage,
Giant Growth,
Protective Bubble