As for hit/expertise - gear to the content. Having both above 0 makes a significant difference to your quality of life and reliability of rotation. Until 4.3 when death strike still heals if it misses, that's quite a big survivability boost too. Certainly shouldn't cap or gem for hit or expertise outside a specific 'threat set', but don't look on all hit/expertise plate gear with the same disdain that other plate tanks tend to.
A comparison of the survival value of Avoidance and Blood Shield can be found in the Advanced Topics section. The short answer is that the relative value is situational and personal. Avoidance will allow you to negate an entire hit, while Blood Shield will shave damage off of many more hits, but in much smaller relative scale per incidence. Comparing on a total damage reduction value, you can take less damage overall with the benefit from Mastery rating, provided that you use DS more than 4.6-5.0 times per minute.