aw crepe

I'm sure the professors will appreciate receiving a polite decline as soon as you've made your decision. What you said above about respecting their work, hoping to collaborate, etc, sounds appropriate. Don't be surprised if they ask where you decided to go and why. It helps them to understand their competition and better communicate to University higher ups the need for better funding packages, faculty hires in a particular area, etc, to win over top picks for admission.

Call!

I disagree! I found out that my application was not complete *only* after logging into my application. A recommender hadn't submitted my letter correctly. If I hadn't noticed, I would still be waiting for a decision that would never come.

I think this means your application is complete, and it's being read by the admissions committee.

Good admit/waitlist etiquette!