If I were to build a zombie deck based on what I think you are wanting to do, this is what I would play and why...
Retrofitted Transmogrant & Gravecrawler gives you 8 Z that can be played from the graveyard ensuring you will have Z to activate Endless Ranks of the Dead since there are only 16 actual Z creature cards (plus 4 Dreadhorde Invasion).
Wall of Souls, especially with Bad Moon, will make them think twice about attacking and give you more time to get established.
Gempalm Polluter can be cycled in the early game for card draw or as a game ender later,, but never play it (and thus it will only count as 2 instead of 6 for your average cmc).
Cemetery Reaper, Bad Moon & Coat of Arms will ensure the Z will be 6/6 or bigger to activate Dreadhorde Invasion and get some of the life lost from the opponent or paid to Phyrexian Arena back... These will also allow you to attack for win or sacrifice any number of these massive creatures to the Altar of Dementia and end the game through running them out of cards. (Just so you are clear on how Coat of Arms works, if you have two 1/1 Z, each one will get +1/+1, so you have two 2/2.. so if you have five 1/1 Z, they will become five 5/5... so ten 2/2 Z tokens become ten 11/11)
Dark Ritual is great for fast decks, but since cards like Endless Ranks of the Dead take a few turns to become established, I feel lowering the average cmc or extending your life expectancy with cards like Wall of Souls is a better option... I also think Army of the Damned cost too much; so its either taking up a wasted card draw in early game or you are already winning from the easily playable and multiple Endless Ranks of the Dead... I dont know how competitive you want to be, but a Demonic Tutor would be nice.
