I can't look at your spec from where I am right now, but will when I can. Blood Tap.... is super useful as it's a free rune. If you've ever hit a rune blackout, you know how nice it is to be able to pop blood tap and get a rune back that is ready to roll. It allows you to "patch" a rune synch issue that can develop. Usual sort of thing is, you have an unholy rune ready for deathstrike and you really need it, but the next rune won't refresh for another 4 seconds. Easy fix. Pop blood tap, hit your ability on demand. Also great for bone shield being refreshed and DnD nowadays.
The main thing with it though is it gives you back a primary resource when you need it.
Blood boil is not your best AoE ability. It's a great snap aggro device for when you're having to collect a lot of loose trash, but doesn't hit all that hard. Myself, even if I have more than 3 targets, I resort to heartstrike. Blood boil is my tool for grabbing mobs like the small scorpions in Firelands. When they scatter, I use it to bring them back.
Death Coil Glyph is the choice if you're running a Lichborne spec. The strength of Lichborne spec is it gives you another cooldown of sorts to recover lost health. EJ covers it well (especially Riggnaros). Basically, you pop Lichborne, and cast death coil at yourself. Each death coil will heal you a fair amount. Talents and the glyph only strengthen this effect.
Rune Strike... it's a critical strike buff. Not our primary job as a tank. Death Strike.... it's a damage buff. Again, not our primary job as a tank, and if you're using rune strike a lot, you won't have much runic power saved up for the bonus anyway. Heart Strike Glyph.... is pretty much a must have. At least in my view.
Again, it's a play style choice. If you're going for maximum effectiveness as a boss tank, it's likely going to be the strongest choice for survival.
More health doesn't increase the amount healed. Not anymore. It used to back in WotLK. Expertise currently has high value due to deathstrike and the deathstrike heals/mastery being tied together. If you don't hit.... no goodies. However!........ if you're gearing for 4.3, it'll be a different ballgame. In 4.3 the heal and mastery will still kick in even if the strike itself misses.
As for the stat priority, you'll get some disagreement, but in general mastery > dodge = parry > stam. Consider, what is the DK's weak point? Taking full unmitigated hits. Mastery helps you smooth out incoming damage. The more you have, the longer your bloodshield will last (theoretically) or at least, the more it will be able to absorb.
Targets? Mastery, you want to aim for 100% bloodshield. That being you get a blood shield equal to 100% of the amount healed. You can go higher, but most DK's will be hard pressed to argue for much less. After that, dodge. Reason why is we get a bonus to parry from strength and if you runeforge with swordshattering, you'll get a +4% parry. Really, the main goal is to try and balance dodge/parry without diminishing returns in either. Stam..... honestly you'll get more as you improve gear. Plus, we do get a small modifier from blood presence, though it is not as strong as the bonus that druids receive.
I've built mine with a focus on trying to balance mastery and avoidance. I'm not chasing mastery like crazy because, well.... at some point, what is 1% mastery really worth compared to a loss in avoidance? You have to remember, DK's can't really "chase" CTC like the shield tanks can.
more mastery = potentially smoother damage and better burst/low frequency attack management (bear boss in ZA great example where this shines)
more avoidance = better mob/trash/high frequency attack management
For a REALLY in-depth view at blood tanking, I'd honestly recommend Riggins' post in Elitist Jerks. It's the second post in the link below:
No. It's not exactly short. He does give rationale behind pretty much everything he talks about and relates it in a way that's very "human". To me, it came across as if he were having a conversation with "me" regarding blood tanking. He doesn't dictate, he discusses. +1 to him in my book.