After finishing Episode 504, start the next feature-length mystery entitled 'Full Score of Fear.' Following this, you can start the 'Magic Files' - the first only contains material from already-watched episodes - which features Shinichi Kudo during his prime. Keep watching Kir's interactions with Conan and Ai until 490, then take a break with an eighth OVA, as well as the second episode of the drama special.
It's the 11th film in the franchise, and it features greedy treasure hunters and a secret cave. After 10 more cases in the 'Kir' arc, 'Jolly Roger in the Deep Azure' slots in nicely.
Seven episodes later, and you'll see a fun OVA the Detective Boys get to face off against Doctor Agasa. The Kir plot continues from Episodes 435 to 452, and then 'Conan' comes to life with the first live-action drama special. When you're about nine episodes in, take a break and watch the 10th movie, 'The Private Eyes' Requiem' and see if they stop an amusement park bomber. Start the next storyline and meet Kir, the latest member of the infamous Black Organization.
