New D&D 5e Campaign. Tips?

[PotatoPlunderer]

I am going to start a new campaign over the summer for three of my friends. The goal will be to reclaim a fortress by building an army and eventually overthrowing the fortress’s overlord. This concept is based off of the gameplay of the video game Middle Earth: Shadow of War, and in the game the strengths, weaknesses, personality, rarities, and even the names of orcish captains are randomized. Therefor, I want to make a table to roll randomized captains with such various qualities.

So here is the question: how can I translate this mechanic into D&D tables?

[Unoriginal]

Make a statblock for the captains, or use one that already exist, and just add/remove/modify traits and stats according to the table.

"Vulnerable to fire", "Cannot be surprised", "Resistant to Lightning", "+10 in STR", "Swim speed 30ft", "Can Sneak Attack", "deals 1d6+STR damages with unarmed strikes", "Frightnened when more than 5 allies die", "use Alchemist's Fire and acid flasks" and the like are a good, fast way to differentiate otherwise identical statblocks.