Character for an upcoming campaign, opinions?

[Arkhios]

I'm going to finally make a new character for 5e game since the last one "ended"/went on undefined hiatus approximately 5 years ago.

Setting premise:
A rather generic fantasy world which, however, once every 10 to 30 thousand years suffers an event called Realm Confluence, where the world drifts too close to other realities of the multiverse. Effects of these events include locations in both realities switching places, and creatures or other entities - even deities - accidentally and unwillingly traveling between said realities, as barriers separating them wax and wane.

Campaign premise:
The characters have been summoned to investigate an odd case of missing people, a previously non-existent mountain, that has suddenly appeared partially on top of, and partially next to, a farm on the outskirts of town, and a cave within.

Character idea:
The sole survivor of a relatively recent event relating to the current confluence, where all of his associates and their base of operations was engulfed by a strange wave of energy that occurred at the moment of a Realm Confluence. Even though the character was hit by these energies only barely, he was left scarred and fell into coma from the pain. A hermit found him, took care of him, and nurtured him back to health, but was unable to cure the scar completely, as it surged with otherwordly energies of unknown origin. The character belonged to an Order of Knights, which is dedicated to archiving, searching, studying, and protecting ancient arcane magic and knowledge. This Order of Templars originated from an ancient elven temple dedicated to Corellon (Larethian), but over the ages, the elves' numbers dwindled and the Order's purpose changed. They are known as Templars of the Tome, but only a rare few of them are actually elves, and even less are religious, let alone worshipers of Corellon. Their purpose has shifted towards keeping vigil over dangerous extraplanar creatures and other threats of arcane origins, and archiving ancient texts and knowledge they believe to be dangerous, especially in the wrong hands.

The character build (so far):
Variant Human, with Aberrant Mark* feat (*renamed Aberrant Dragonmark, obviously because this setting isn't Eberron)
Knight of the Order background (obviously).
Class is possibly paladin, or the Arcane Paladin variant that I've been working on lately. Likely with the Oath of Watchers, because it fits the concept very well.
However, since his accident, not only his body, but his soul is scarred and tainted by unknown energies, and he is desperately seeking for a cure, and is willing to take it to extreme measures.
In this campaign, we will be utilizing the 3rd Party Grim Hollow Campaign rules by Ghostfire Gaming, and I've discussed with my DM that my character will eventually begin transformation to a Specter, because of his scarred soul.

As for the stats, as I know you'll ask them eventually, our group used a "6-by-6 grid" method, in which all players roll one set and the DM rolls the missing sets, writing them down on a paper so that the rolls form a 6 by 6 grid. Then the players choose the one stat line they prefer either diagonally, horizontally, or vertically: 18, 16, 15, 14, 13, 10

I'm a strong advocate of making characters with the ground rule that they have to make sense. I really don't like builds that have been made purely because of Power.

So, understandably(?) I feel rather filthy because I've started to think about a Paladin (Oath of Watchers)/Warlock (Hexblade), which might actually make sense on so many levels, with this concept.

From Paladin (Oath of Watchers) I feel the most important abilities would be their Channel Divinities and for relatively obvious reasons, Aura of Protection, but beyond that I feel I could live without them.

However, from Warlock I wouldn't really need much more than the Pact Boon of the Tome, or if I'd give in to my urges, two 4th level spell slots/short rest.

What do you think? Should I stay single classed paladin work out the struggle through roleplay, or multiclass with Warlock as "an extreme measure" to seek aid from an Otherwordly being such as the Raven Queen?