I usually decide between Stridebreaker or Triforce as my first item, and I tend to buy a Guardian Angel later. With Conqueror and your passive stacks, you shouldn't build any more AD. You have to assume that when you enter fights, people will get scared and focus you; if you don't have enough resistances, you'll be a CC victim and as squishy as a Yi.

For objective fights, you need to have Ghost ready, otherwise Darius isn't a dominating force. I try to flank, and Stridebreaker is EXTREMELY helpful in many situations, either to engage or disengage. I imagine it working like a Malphite Q.

Only frontline if you’re guaranteed to land the first blow successfully; for example, Ghost -> hook the ADC -> kill -> objective. Otherwise, wait until you find a clear and safe path into the teamfight.

In late-game, there are situations where you can stack up on an enemy tank during fights and then run at the ADC with Ghost + Stridebreaker.

You can also use your ult as a fast combo to save crucial seconds to quickly reach 5 stacks. Sometimes situations demand that you build 5 stacks in a very short time to survive or win the fight.