I'm a little surprised you wouldn't have already gone and read up on DK tanking in Cata.
Go now, and reap the benefits: http://www.tankspot.com/showthread.p...-Bloody-Future
That done, I'm surprised that someone finally picked mastery outright. So for gemming/reforging I think you've done alright. There's a lot more information over at EJ that you also might find to be helpful: http://elitistjerks.com/f72/t110102-...e_tanking_4_x/
@your questions -
1. EH is not bad. Stamina is not as important anymore, but its still up there. Mastery seems to be the more solid choice in terms of avoidance/mitigation, with dodge/parry coming in a close second. You probably won't need to actively seek stamina until you hit heroic raid content.
2. Trinkets are a fight to fight basis, but as mastery is pretty awesome it doesn't hurt to use it. The trinket from Tol Barad is considered one of the better mastery trinkets in the game.
3. Constantly use RS as it has a 45% chance to activate a "random" rune that is asleep. It keeps your runes flowing. Because you can choose not to use your second blood rune (and maybe use Blood Tap and then another ability after) you can pull up one of the runes that you just used on Death Strike. DS is your most important rune ability, especially when you are stacking mastery.
4. The Strength bonus from Aboms might is pretty small compared to the bloodworms. The only reason to take Aboms might is if your raid does not have the 10% attack power bonus. The Bloodworms have a much more noticeable effect and combined with Vampiric Blood and other healing effects, they can really add to your healing done. That and the fact that they smart heal anyone close to them is an added raid benefit for your melee.
4.5 Yes. Crimson Scourge is good for AoE and for a small runic power benefit from the free BB procs, but you're also probably able to take the points from Aboms might just as easily.
5. Haste has an impact on rune regen, that's true. It might not be greater than the avoidance/mitigation you get from other enchants. There isn't a whole lot of math on the haste as a valuable stat, so I can't comment on its effectiveness.
There are a lot of DK tanks that do not use Lichborne, which is fine, but if you are looking for another survivability cooldown, this spec - http://www.wowhead.com/talent#jcGr0sMruszG0obZ0b:so0zk which is made for 10 man (interrupts needed) gives you all the survival points. The Lichborne macro is as follows:
/cast [@player] Death Coil
So that when you use it, it Casts Lichborne, and then Death Coil on yourself for the healing benefit DC gives to Undead. To get the full benefit from this, you'd need the DC glyph, and to be at 130 RP ahead of time. It is a very planned CD, so it takes a bit of practice to master. Using VB at the same time can also greatly increase the healing from this CD.
That's all I have without rehashing a lot of what is already available both at EJ and in the Guide by Satorri.