3 stacks of Haven + Undying + lvl5 Strength of Stone yields a total 47.667% damage reduction when all in effect (due to diminishing returns). In other words, total damage reduction will fall at 37.264% when above 40% health, and then drop an additional ~10% when under 40% health due to undying. Some would argue that this is not the most efficient use of loadout points, which is arguably correct. You technically can stack more loadout points onto other cards for other abilities, but I choose to opt for damage reduction regardless, mostly because Terminus truly needs the damage reduction more so than other tanks due to his limited range.

you can either do 3 or 4 stacks of It Follows, along with 4 or 5 stacks of Playing God. Personally, I don't think Playing God yields that much health recovery to be worth it, so I typically will do a 4:4 split between the two.
Nimble and Terminus go well hand-in-hand due to his limited range. Once you get your calamity charges, you'll be incredibly fast. With Terminus, I find I don't frequently get kills unless the enemy flankers are contesting the point. So I opt for lifesteal to help with sustain. And lastly, cauterize is extremely useful in teamfights where you and the enemy tank are whaling it out for control of the point, and the enemy healer is attempting to heal their tank. It frequently becomes more handy than one would think.