It is important to reach hit cap (6% , or 5% if you are with Draenei) to never ever miss a taunt
Besides that, going for full stamina is almost always better, especially in Lorda since bosses hit extra heavy.
Some little improvements:
- The +10 stats gem on your head is very bad. DPS classes use this gem because it's their "least bad"" option to activate the meta-gem colors, but as a tank who uses an austere earthsiege diamond, you only need blues and ONE red to activate it, so you should probably simply use a purple gem somewhere to activate it, you'll overall gain a lot of stam from this.
- The shoulder enchant: you could use the enchant from stormwind pvp vendors which has resilience and stamina, it brings you more stats overall
- Weapon enchant: forget blood draining it does very little against massive boss swings. Mongoose is a good option, or a simple AP enchant if you're poor is fine too.
- Rest of enchants is ok
- Profs: JC is BiS so good choice. Blacksmithing is also a good prof, but if you're looking for "the best", engineering is better. The nitro boots will change your life as a tank, and the +885 armor enchant on gloves is massive.
For all the other gems you mentionned, and mostly green hybrid gems: They can be a good option if you are under defense cap, or under hitrating cap, but if you have reached those caps you're better off using pure stamina.
Extra hit and extra defense bring very little compared to extra survivability from pure stamina.
For extra aggro:
It is much much much simpler to simply use a strength libram when you have aggro issues, than to try to gem your way out of it. You'll be sacrificing some dodge, but dodge is not really a vital stat.
Most probably you'll be paired with a DK that has unbeatable aggro, so don't focus too much on that, you let the DK do the aggro job and you'll be taking it back with a taunt when needed.
As a general rule of thumb for tanking on Lordaeron: you want to make yourself as tanky as possible first, and experiment later when you have better gear.
That means the stats you should be aiming for primarily are:
defense until cap (540 or 537 if you use this resilience shoudler enchant ) > hit rating until cap > max HP / Max armor >>>>> dodge > parry > block > aggro stats (STR/AGI)
for the expertise question: expertise isn't really a tanking stat so try to avoid it in your normal gear. That being said, some bosses require extra high expertise to not get blown up, so stock up some pices for when the day comes, because when you'll tank Sindra or Halion, you'll need to reach 56 expertise
Another thing I see some tanks missing is that extra armor makes a world of difference, so you should 99% of time using the pieces with extra armor on them. example: t10 chest and gloves have extra armor, the legs "Pillars of might" have extra armor, the 245 ring sold by the EoT vendor has extra armor on it too etc. Those are your best starter pieces as a beginner tank because it really lets you pucn above your weight.
source: played prot pal on lorda over most of the content