We've been regularly doing Tong for a while now with our in guild groups. Many many combinations have been tried, as well as item levels from 11-17k in many cases. So a lot of the possible scenarios have been covered and can be directly compared.
While not a step-by-step guide I wanted to lay out some tips on item level that we've found help in this dungeon that for Mod 12-13 is so central to everything we do.
This is a central point of confusion, not helped at all by the contention of the devs in an early livestream that it can be done with a group of minimum item level, i.e. 11k. It cannot. Barring extreme exploits, and especially with the mod 13 nerfs we have tested low item level groups extensively, and further have never seen any proof that this is doable.
So what is doable?
There are different scenarios here depending on classes and IL. On average you'll want your group to be in the 15k area to have a reasonable chance of finishing. Still some fails, but its worth a shot. Yes its possible to get a (as in 1 per group) 12k through there of certain class types. You will probably have to make up for where they lack somewhere however.
DPS: Generally every group does the 1 DPS 4 support route here. We've gotten 12k DPS through, which you can do with enough boosting and a competant DPS player. Clearly higher is better here.
GWF, TR, GF, and HR are the preferred DPS, generally in that order. (Many would put GF higher in the list, feel free.) CW is possible, but is at a distinct disadvantage compared to the other DPS classes after the mod 13 changes.
CW is only really viable as DPS at 15k or higher. Note: As a skilled DPS cw, the author makes this observation with disappointment and not with a general bias against the class.
This is the real 'secret' to doing Tong. Take any DPS and add 2-3 mega buffers and 1 good defbuffer/buffer and you'll go far. Often there are 2 DCs though after mod 13 especially, other combinations are viable.
OP - A good power share pally is the most common foundation. After 12k surviving isn't really the problem so much as giving the rest of your team enough buffs. 15k+ for good power share definitely recommended.
MoFcw - Master of Flame debuffing support is by far the most common position for a CW in Tong. They provide some of the most debuffing of any class. At the same time to get those debuffs doesn't depend on IL. 12k+ is doable as the debuffer without feeling like you're just being carried. Any damage you do is a bonus.
DCDO - Most groups still go with 2 DCs, though other combinations are possible as well. DO buffs/debuffs don't depend on IL so this is the position for the weaker DC in the group. 12k+ recommended. This player is essentially there for the Hallowed Ground daily, and Terrifying Insight passive. Other damage and/healing is a bonus.
ACDC - AC buffs like Anointed Army do benefit from higher item level. The main job here is to power share with AA. Other skills are bonus and complementing with the DO is even better. 15k+ recommended.
SW - Feat, curse, and encounter based debuffs dont depend on IL. So lower item level is acceptable here. They do have a power share based on their power, so higher IL is preferable. These can also help keep people alive through their heals as templocks (generally the only version used in Tong). 12k+ recommended.
GF - Excellent, almost indispensable for the speed runs seen in videos. Their running boost takes the team through the long hallways of Tong, cutting down on the marathon between bosses. They can buff excellently, and do excellent DPS. They can be buff/debuff at nearly any item level so 12k+ recommended, dps requires higher IL.
TR - Initially overlooked, a TR can be excellent support while at the same time as being backup DPS. Il helps here, but a skilled TR can self-buff decently well. 14k+ recommended.