There’s a woman called “The Kitten Lady”. She rescues and hand rears kittens and has a plethora of info and YouTube videos. Kitty Zee has given you great wisdom herself
Unfortunately, FKS happens sometimes no matter how hard you and kit fights.
I don’t have a preference between feeding them KMR (or other kitten formula brands) or Goats milk formulas. I’ve used both and the only differences I’ve found is commercial formulas tend to cause constipation and the goats milk one caused looser sometimes watery stools.
If you can pinch the nape if the neck and it doesn’t quickly fall back into place quickly, little kit is/is becoming dehydrated. If their gums are wet and robust in color, mix their formula with plain pedialite instead of water. If gums are dry either take them to an emergency vet or if you know how, give kit a subcutaneous syringe bolus of fluid…Kitten Lady has videos on this.
Now, that being said, I’ve only done this kitten thing twice. I’m not an expert or a professional.
I wish you luck and send my biggest, warmest kitty hugs to you and little one