You're a good patient "doula", Seb. Isn't that what a labour coach is called? Hope the next one is all right.
A litter of 4 is average, but I had a queen that had 6 one time, but she was quite big. Hope the one (little boy or girl?) is showing interest in nursing. Occasionally a kitten will start to nurse initially, but then show lack of interest and fail to grab the teat and suck, and will actually crawl away from momcat to a corner of the box, and if brought back, to mom will do it again. This is "failure to thrive" and there is nothing that can be done for it. Nature has a reason for it not to survive and natural instinct in the kitten makes it crawl away from the litter so it doesn't contaminate the rest---at least this is what would happen in the wild.