https://eu.battle.net/forums/en/wow/topic/2504881097
https://www.youtube.com/watch?v=S-XnYZv2Kis
These are two great guides I could recommend taking a look into if you specifically going to Roleplay a Death Knight.
As for guilds you are aiming for Alliance I presume I have set up a small gathering of guilds I can recommend.
Night Elves are indeed slightly ‘‘more complicated’’ to roleplay due to the nature of their race but I would only recommend you to try to read more into the specific lore of their race instead of encouraging you to step into another race instead if that is what you want.
< The Ebonsworn >
‘‘Dark Protectors of Azeroth’’ type of guild. We combine the ‘‘Brotherhood’’ vibe of WotLK and the ‘‘Military’’ side of Legion. We are a ‘‘Acting Unit’’ of the Ebon Blade roaming areas to serve the Ebon Blade’s interest. Short in short we do ‘‘bad’’ stuff to achieve good things.
< The Dark Grail >
Lawful Evil Order of the Ebon Blade. While they see their duty to protect the living, they do not see it necessary to be involved with them beyond protecting them. They rely on their vows and duty to the Ebon Blade instead of morals.
< Ebon Ranger >
Chaotic Neutral/Good Ebon Blade affiliated group, aiming to maintaining the balance between life and death with their forces mainly focused on Shadowlands and what lies beyond the veil. Working with the living is not an issue for them yet they are well aware that the living might not approve of their methods. But they do what the living cannot and they will continue doing that.
https://www.argentarchives.org/search/node/Ebon+Ranger
< Hand of Thassarian >
The guild is an Alliance-based undead concept consisting mainly of death knights, yet other out-of-character classes are welcome as long as the character, in-character, is an undead, or uses powers of the undead – such as necromancers, et cetera. We are creators, and joiners of both large and small events, and participants of war campaigns. The events include training days, travelling, missions, and cross-faction warfare, either guild only or other guilds and communities. As we are an event and campaign structured guild, we do also have casual roleplay within and about Deadwind Pass, and within the main Alliance roleplay hubs – Duskwood and Stormwind City.
< The Crypt Seekers >
Not a company consisting of the undead alone, the Seekers’ cadre of Ebon Blade members is still rather sizeable. A group of adventurers and treasure hunters, they also do the occasional hunt for rogue necromancers or other common targets of the Ebon Blade, thanks to their leader being a Death Knight. The Crypt Seekers are not fully affiliated with the Alliance and are neutral towards the Horde. The group’s general alignment also can best be described as true neutral; The main goal being to always keep their own casualties as low as possible while making the largest monetary profit they can.
https://www.argentarchives.org/node/233521
< The Eclipse >
Soldiers of the Alliance, living and undead whom march a bleak path, working under the wing of an Ebon Knight with unwavering loyalty to the King and Crown. Despite this they share a code of immoral edicts, posing no qualms with studying nor wielding eldritch darkness.
https://www.argentarchives.org/node/233521