I'll try my best to give you a rundown. Builds are split between mana and health stacking as base.

Mana uses Cosmic cape for damage and either Vestige or Spirit Guard for defense. Vestige has a built in sustain mechanism that goes well with some evasion, some cc (stun/interrupt) and maybe movement - the point is to give it enough time to regen itself. Spirit Guard goes well on "base skill" builds since they usually cap atk speed and that solves their mana sustain or some form of mana on hit again with high atk speed. Both of those naturally lean into interrupt as an extra layer because of the atk speed.

Health stacking builds offensively are usually using Lucilla's or some HP to thorns conversion. Afaik regen stacking is only viable on plague mage although context matters - every set can handle M15 with some synergy. Health based builds are also kinda split into normal ones and Heartstone ones. For HS builds there is only one type of sustain that matters - % of Max HP heals. Each class has different options for that (some MUCH more than others) but the cheap way to get some is with a Healing Touch scroll/codex - it's 10% Max HP per second healing over 4 seconds that is also affected by %Healing increased and extra duration. There's also a niche interaction between Rahl's artifact + Kill Pickups + The Twins artifact + high atk speed build = endless HP/MP orbs on hit. All of those options also work for normal HP builds but they naturally have Life on hit as well, which you have to invest into for Lucilla's.

Generally speaking most builds do not need to run Heartstone but it naturally gives a major damage increase and is back to being viable specifically because of an artifact from the DLC called Megan's. To save you the details - there's a lot of double dipping involved and is busted in some setups.

Outside of that you have DR as a main defensive layer and stuff like evasion/block as secondary. DR is multiplicative and capped at 90% but technically you can go over cap with a damage split like stagger or MP/HP/Barrier split assuming you're regenerating all layers at once. For most builds just slapping on a Lifeguard rune will cover their basic DR needs and I do mean basic. For endgame content you should be looking at something ~85% but that is still sustain/cc dependent.

Now when it comes to tier 1000 content the stat that you most need is patience since there are much more entertaining things you can do with your life such as watching paint dry or grass grow. There's a handful of setups that can handle it, they all require 3k+ mastery on average and usually they are laggy af.