Can’t get in to dark brotherhood

No, none of the Dark Brotherhood's quests intersect in any meaningful way with any other quest chain. Some targets may have minor 'radiant' quests available, but none are significant in any way.

The worst thing that can happen is you can end up with a very large bounty on your head, which could make completing other quests... difficult at best. However, this is both a solvable, and preventable problem.

The only collision other than the one you've noted, is that

Vittoria Vici, the target of the main-line quest Bound Until Death is also involved in the incredibly minor quest The Spiced Wine.

Having completed the "Innocence Lost" quest, I immediately fast traveled to my house in Whiterun and slept for 1 hour, the kidnapping took place straight away, there was no delay.

It has been noted on the wiki that:

If the courier doesn't appear after waiting a few days, sleep in a bed for at least 8 hours and the quest will continue.

• Sometimes this can take several days, even with sleeping.
• If the courier still does not appear, try fast traveling to a different hold and waiting.
• Sleeping for at least 8 hours is not necessary. 5 hours continued the quest. (PC) 1 hour continued the quest. (Xbox 360) 1 hour worked (PS3)

Just keep wandering around a different town and waiting until the courier arrives, it's been suggested this can take many days in game.