After doing a lot of reading, the general consensus is that it is 100% normal for babies to need a nighttime feeding at least until they are 6 months old. 4.5 months seems way to young.... We did Ferber, but not till our son was 8 months old. I read the Ferber book, and he has a general guideline of not sooner than 6 months.
I do think that you're going along the right path. Any time you can start the self-comforting process, it's a good thing. But for me, a baby younger than 6 months is just alone and scared in the world, and is crying because that is pretty much the only way they can get help.....
Our problem was that my son associated rocking/nursing when falling asleep, and when he rose to the light sleep stage, he was aware enough to look for that and want/need it to fall back asleep. That was hard, at 2x per night (or more as a very young baby), and I was so happy when he went to 1x per night. But he starting, around 8 months old, waking more frequently rather than less, and it got too hard, with 3 or 4 night wakings, and me having to sleep on the couch (because we don't co-sleep due to DH's issues with insomnia and my desperate thought that bad sleep was better than no sleep)... Anyway, we did it--it was hard on me, and on my son, but it was worth it, and I'm glad we did it.