I have eliminated most of the builds initially posted since they have low stats, and the selection has boiled down to 3 of them, 2 using healing staff on the back bar, one still using 1H+S.

1) Bloodwspawn, Bright-Throat's Boast, New Moon Acolyte front bar & Maelstrom Restoration back bar with Radiating Regeneration, using Spring-Loaded Infusion to get more Stamina & HP. The build has 1638 magicka recovery which is more like ~2000 considering the returns from Radiating Regeneration, which are quite reliable from my experience if I keep it up on 3 or more people. Spell power is 8.5K. I also changed the ghost morph from Intensive Mender to Spirit Guardian because I rely more on Radiating Regeneration for HoT and I'd rather have the damage reduction.
https://en.uesp.net/wiki/Special:EsoBuildData?id=218721

2) Bloodspawn, New Moon Acolyte front bar & Shroud of the Lich Back Bar and 2/3 Willpower jewelry for extra magicka - I can also use 2 Potentates for damage reduction, but I'll have to transmute those to Arcane or Infused. This will be using Bewitched Sugar Skulls for extra HP & Stamina - it also has about 900 HP recovery but it shouldn't make much difference. Magicka recovery w/o Lich active is just 1400, but when it's active, it increases to 2950. Assuming it's activated every minute (the cooldown is 45s), and it lasts 20s, the average recovery will be ~1900. On this build I will keep on using Intensive Mender, but also supplement it with Combat Prayer for extra burst heal and group buff. Considering Minor Berserk from that skill, it will have 8.9k spell power
https://en.uesp.net/wiki/Special:EsoBuildData?id=218691

3) Bloodspawn, Bright-Throat's Boast and Ancient Dragonguard, using Spring-Loaded Infusion, 22.9K HP vs. the others, that have 21.5k and 22k respectively, slightly lower magicka recovery, only 1650, but also no increased skill cost, which should balance out. Above 50% HP: 7.5k spell power on front bar, below 50% HP: 6.7k spell power, 30.2k spell & 28.4k physical resistance (35.2k & 33.4k with Resistant Flesh, but also defiled).
https://en.uesp.net/wiki/Special:EsoBuildData?id=217507

I will be testing the general skill setup and combos using gear borrowed from another character, having sustain & damage stats within the same ballpark, to see the general sustain & combo effectiveness then decide which one of the above setups I will craft and use subsequently.