For the sake of not hurting your eyes, I changed the glyphs and marks =)

I also added to the Buddy List, Nunu and Katarina, aswell as removing the all health runebuild suggestion. I decided to leave the point in Greed - but gave some explanation as to why. I might not use it much, but i feel it warms my heart in those cold games filled with semi-******ed teammates =)

- Do tell if something else catches your eye..

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i agree with Ixilliana, but please change the marks with the glyphs, that hurt my eyes ;_;

first of all, great idea bro, making a guide that is actually made for low ELO, leveling your summoner and learning to play. Further more it is a guide made for a tank, and it isn't focused on having a game that looks like this 100,000/0/0, we have too many people striving to achieve that in low ELO.
well start with the bad cons.
i don't think switching all your runes with health runes will help, neither early or late game. The increased amount of health will not last as long with the mitigation you have to give up. second is that you have to give primary runes up for secondary runes, and this is both for marks and glyphs if i'm not too wrong.
i don't think greed is that important. It only gives you 240 gold for a 40 mins game. it can help u getting that first item a little faster, but usually will just make u stay in the lane a little bit longer, if i am right (long time since i've been playing amumu). if u feel u need to get "Blink of an eye" or "Awareness" in the utility spent a point in greed too, else use the points for some more tankishness or some more AP.

as you describe him at lo ELO he doesn't have an easy way of last-hitting creeps though this is something needed to be learned with most early game low damage champions. by that it seems wise to create both HoG and PS as they also give a decent amount of health and mana & health reg early game, their GP10 combined is 10 times as much as greeds (2400 Gold within 40 mins), and they can further more be upgraded to Shuralias reverie (dunno if it's spelled right) and Randuins omen. both of the items makes great sense on Amumu (especially with their uses).

an add to skills that goes well with CotSM could be both Nunu's and Katrina's ultimate, though later on Nunu and Amumu wouldn't usually be on the same team, since they are both great junglers.
furthermore i would think that amumu is also a great counter for nunu, katrina and fids ultimate (as far as i remember all of them will be interupted by a stun, in case Katrinas and Fids arent it will give the team time to get out of the ult. bandage toss can get in fast without wasting health due to the range of the ult's.