This isn't going to be a very comprehensive review, just some personal observations.

On the plus side, the line work is excellent - confident, straight, accurate. And you've clearly got the hang of construction method and forms look solid. I think a lot of flair in the details.

What is letting the drawings down are the basic proportions. The birds, fish and reptails are fine, with the mammals there are cases where the legs look too thin or the neck looks too long.

I had a quick look through the Lesson 5 notes again and I realised there is really much guidance on the matter. The notes might mention how the ribcage is about half of the torso, but when it comes to judging how long or wide the legs are, we are left to eyeball it. The course covers this in Lesson 7 with vehicles in which it may take the wheel of a car as basis and then measure out the lenght and height of the car in terms of how many wheels they span. I guess you could try taking, say, the head of the cat in your reference image and use that to get a sense the overall dimensions of the animal?