If you are having trouble with threat generation you want to use Haste. If you are having trouble staying alive you want to stack more mastery.
No, if you're having trouble staying alive you want to stack more haste. Haste is our top survival stat. Avoidance are our worst stats (except for crit), yes avoidance procs grand crusader but the benefit is still very very small. No matter how much avoidance you stack it will not give you as much holy power or survival as haste or even mastery will, and even without stacking any avoidance at all you'll still get a good amount of procs anyways. Unless the ilevel gap is very large haste gear is always going to be better than avoidance gear.
I prefer using Eternal flame over SS. But people say that sacred shield does more dmg mitigation.
That was the last 2 tiers. This tier EF is much better than SS except for in a handful of niche situations. You don't really even need to pay much attention to your bastion stacks most of the time either because if you're performing the rotation properly you should be guaranteed to have at least 3 stacks of BoG before you need to refresh EF, and while more stacks is better, keeping it up all the time is more important. So all you really need to watch is your holy power because you only want to use EF with 3, but you should be watching your holy power regardless.
Also, ideally you should try to hold your SotR until you have 5 holy power so that you always have that 2 extra for emergencies. Which is especially more useful when using EF before you have the 4p (in case you need to use SotR and refresh EF quickly). In addition, Consecrate is actually typically our lowest priority filler spell, unless tanking a group of adds, it's not bad, but our other abilities just hit harder (more threat) against a single target.
If played well, tankadins are quite solid. I see no reason why a 510 tankadin shouldn't be able to tank SoO LFR without anybody knowing he wasn't 520.
Oh, also since it wasn't mentioned anywhere that I see, as tank you should always be using seal of insight, always. It's a huge source of self-healing and worth way more than pitiful amounts of damage that the other seals do.