Block value dimishing returns on shield slam (your main damage ability) really kick in around 2.4k block value. So if you keep it around 2.1k-2.4k would according to my experience be optimal. If you are going to go pure prot PvP, enchant all out-strenght if you are hit capped for PvP (I believe hit cap in PvP is on 5% on targets with no defense on gear), but also make sure your metagem (the one with 5% increased block value from gear) is working. Defense is something you gain naturally through gear with BV, but do not enchant or gem for it. Defense is however cool as you gain a slim chance to be missed. There is nowever not possible to be 'crit immune' in PvP, so going defense for that reason is pointless and impossible.
Expertise is meh. I guess it can be usefull for killing casters in some situation, but you will hit lots of them when stunned and very often from behind meaning they cannot dodge anyway. I'm currently at 18 expertise (about 20, or 5% reduced chance for target to dodge is the 'caster cap') in my pvp gear, but I've started to ignore the stat and take it if it comes with something else I need more. When facing rogues, hunters or anything that gains dodge through gear the amount you need becomes too high to be something at all worth it to go for.
Resil I guess is debateable. You get a natural 10% damage reduction in PvP through being mostly in defensive stance, and that seems to cut it for me. I never die first in arena, my healer does. However it does make you a meatshield of another world. I so far gear for block till 2.1k-2.4k (about 2.3k now, and staying there) and take PvP pieces in my other slots. Through that and gems I'm hitcapped. The PvP pieces I got add some resil (170ish), but is largely negligible. I,in 90% of all duels so far, beat prot warriors with arms pvp gear and ridiculous amounts of resil and crit through gear, so I've chosen to ignore it and take it where it comes naturally.
As for enchants in general, gem hit till capped. Just make sure you are always capped. Other than than, strenght is imo optimal(I've spared one yellow slot for the 20 resil gem however). A few of my pve pieces goes into my pvp set however, and those I've gemmed and enchanted to have a use in pvp and be 'passable' for pve, meaning hit and stam (on conq chest) is 'passable' for pve and also has its uses for pvp.
Attackpower and crit is what I prefer enchanting for (on legs, head, bracers, hands if not an engineer and some other factors and so on). The only place I've not enchanted for attack power and crit on my pure pvp pieces are shoulders (I consider 30 stam and 15 resil superior), boots (minor run speed increase on Tuskarr's vitality, which is AWESOME!) and hands (I'm an engineer).
Basically, you want things to boost your general damage (being block value, strenght and crit as mentioned) while maintaining hit cap. Other stats are merely bonuses (resil, stam, defense, expertise, dodge/parry). Deva will be your bread and butter, so get a slow mainhand as well. I know some will argue not to, but the general increase in damage from a slow mainhand just outweighs the benefits of a fast mainhand.