Hi fg, {{hugs}}} welcome to the boards.
Your Lo falling asleep mid-feed is pretty normal at this age and by the sounds of it your doing the right thing by changing the nappy to wake her up again to feed.
When I was in hospital the midwives told me to stip Calum to his nappy to keep him more awake or rub his palm.
You can start the routine as early as you like, I am not sure if you have seen the FAQ's in the EASY boards
https://babywhispererforums.com/index.php?board=82.0 in particular;
S.L.O.W. down (and Appreciate your Baby's Language)
Getting started - how I survived the first 3 months
What is EASY?/ The benefits of using EASY
Starting EASY with a newborn-What to Expect
***HOW TO START YOUR BABY ON EASY***
You can also find EASY logs to download, routines and information on the 5 temperaments a baby can adopt (may be a bit early for you to decide yet)
I would also suggest putting her on a 3hr EASY to start with and she how she goes.
Lauren