Does this sound like beginner's advice? Then you'd be surprised how many famous scholars come to me with end notes that are a mess, and without complete certainty that x set of notes came from y archive. One stopped by recently with over 500 haphazard citations and a pitiful question, "Will someone in your office please check all of these for me?" The answer is of course was no (it would take months if not more than a year of quite a few hours per week from one individual), but someone must do it before his book is published.
How do you eat an elephant? One bite at a time! If you do just a few citations as you write, you'll get there, and you'll be so relieved not to have to face it all at once.