Templar is the worst class you can pick for PvE tank, since it doesn't have any skill that unconditionally restores stamina. More so on a magicka Templar that has a very small stamina pool. You can slot Repentance but that will only work if you have something to repent. And if you have any Stamina Templar DDs in the group you'll be fighting over corpses with them, since every corpse can only repented once, and the healing scales to your highest stats, which he probably has.
Shields, meaning Harness Magicka, since Blazing Shield scales to your health, so it will be much smaller, only really work if you are tanking trash. They won't help you at all against hard hitting bosses, since most of those attacks do much higher base damage and they also have an added CC/stun/knockdown. That value is >100K for some DLC dungeon bosses. Tanks can get away by blocking, if they have stamina for it. If you shield such an attack with ~15K harness, it will still amount to 85K, since shields are subtracted first. If you are resistance capped - maximum 50% mitigation at 33K resistance, so Pariah is useless since you can hit those numbers easily if wearing 5 pieces of heavy armor, and most of the resistance added by that set at low health will be wasted - and have CP invested in Hardy/Elemental Expert and Ironclad, you can get ~10-15% on top of that -
they go up to 25% but they are not additive to the mitigation given by armor. So you'll still eat >30K damage if not blocking. Which will most likely one shot you, since in more difficult fights like Velidreth in vCoS, you will also have DoTs, healing and even resistance debuffs on you, meaning you'll rarely be at full health. Unless you know the mechanics very well in those dungeons, you'll get rekt hard. And that's like a stroll in the park, compared to Earthgore in vBF, that splits into 3, each of the adds hitting with similar numbers within the space of 2-3 seconds. When tanking all 3 I gasp for resources even on a DK tank spamming ingenous shield - it doesn't really do much for me, but at least it restores stamina while blocking and shields other group members - and hitting Aggressive Horn every 45-50s - DKs also restore resources from ultimate use.
I still don't get it why people still want to tank on Templar post Morrowind. With the upcoming block cost increase due to formula change - shield play glyphs will be considered before sturdy and other % reductions - DK and Warden will become the only viable tanks for hard content. https://forums.elderscrollsonline.com/en/discussion/389032/pve-tanking-discussion-for-dragon-bones If you still want to try it though, I recommend using standard tank gear: Ebon Armory (more health for group - Crypt of Hearts), Akaviri Dragonguard (cheaper ultimates - overland Eastmarch), Swarm Mother (good monster set for classes that lack pull abilities - Spindleclutch 1), Torug's Pact (higher resistance debuff from crusher enchant - crafted), Hist Bark (really good for beginner tanks, effective 15% mitigation and bock cost reduction trough dodge chance - crafted). Ideally you should combo 5 Crafted 5 Dropped and a monster set.