I'm fairly new to magplar. Coming from other classes, I did not like the templar's "in your house" playstyle (meaning you stay in or near your rune). I like speed and mobility, and I'm used to shielding. My build is still changing, but if you like the same, you could try this:

2x Mighty Chudan (or Skoria, or maybe Blood Spawn, take your pick)
5x Shacklebreaker (or could try Amber Plasm, if you have it)
4x/5x Prisoner (Prisoner 5-piece only on front bar)

5 light, 2 heavy. All impen, all prismatic enchants.
All stats into magicka, leading to 38.6K total magicka, and 21K health in PvP.
2x mag regen, 1x spell damage on jewelry
Mage mundus (better shields)
Race: Breton / High Elf
Food: Ghastly Eye Bowl

Main bar = dual wield. Nirnhoned gold sword in main hand, Infused or Sharpened off hand (purple sufficient). Magicka damage / magicka return and magicka damage / stamina return enchants.

Puncturing Sweeps
Honor the Dead
Inner Light
Radiant Glory
Harness Magicka (8K shield from 38.6K magicka, with 66 CP into Bastion)
Dawnbreaker of Smiting (don't have Soul Assault or Meteor yet, but DB works well)

Back bar = resto staff. Infused with berserker enchant.

Toppling Charge
Extended Ritual
Degeneration
Purifying Light
Healing Ward
Light's Champion

I'm quite loving this build at the moment. The potions are either Immov / Detection / Magicka, or Immov / Speed / Stamina. Both work. Sustain is good. 12K (4 x 3K) unbuffed single target damage from Sweeps, in CP. 41% crit. 19K / 26K resistances.

The Prisoner set might take some time to appreciate. At first glance it looks like a sustain set, but that's not really what it is. The most significant thing about it is the 50% sprint cost reduction. Together with Shacklebreaker you have a 16K stamina pool. This means, unlike a "regular" magicka toon, you can sprint quite freely. The mag sustain from it is great, as long as your gameplay is broken up into small fights and you sprint inbetween. This happens quite a lot in Cyrodiil, so I love it. Don't expect the set to be much good if you are focused though, or in a duel against, say, a DK who likes to lock you down. The build has quite a large magicka pool and decent 1.85K mag regen for that though. I find you need that mag regen. The Prisoner set avoids downtime between fights and gets you around quicker, but in a prolonged brawl you'll still rely on the mag regen and occasional heavy restos, especially if you are only up against stamina players, or you choose to ditch Harness for Dampen.