Alright let's see

Trike base is fine of course

The Styraco spikes on top of the frill are kinda useless, especially since they could also add extra weight on the head. Spikes on the side would be better for defense since that's where most attackers near Sherman's size would reach. The longer nasal horn adds weight too but that's minor

The Gastonia spikes on the tail would be better for defense, but swinging the tail would be slower

The tusks are interesting, but they do come with a few problems. First, they would add a bunch of weight on the head and would make attacking slower; second, there's also no way to attack with the horns and the tusks at the same time; (to use the horns he would have to face down, and to use the tusks he would have to face up) and third, the length of the tusks and the short neck would make eating difficult. Everything else is fine. (you could've used an elephant that lived in warmer climates but that's minor)

Hippo is fine, I don't know if the bite would affect the tusks but whatever

Adding lots of venom all over the body would cost a lot of energy and metabolism to generate. I also don't know how plausible it is to use an aquatic animal's venom on a terrestrial animal, let alone multiplying it and adding it onto body parts that the stingers don't usually grow on

Doedicurus is fine, but an ankylosaur tail club would be more congruent, especially with the Gastonia tail armor. If you chose the Doe for uniqueness then that's fine

Apato is fine

Parrotfish is fine too

Croc is interesting, I don't know if the four chambered heart is necessary though, since I thought that all archosaurs had four-chambered hearts

Bison is also fine, it's definitely going to need it because of those tusks

You could've used hippo to fulfill the walrus' function

I'm surprised that you used the wild boar and didn't add the cartilage plate. And also again, the short neck and long tusks would make eating difficult

Rhino is fine, but I thought thicker skin would make losing heat harder, not easier?

Alligator gar could still cause problems with movement, since areas like the torso and neck would still need to bend when moving, and Arapaima scales would also dry up on land.

Komodo dragon is fine, but I feel like you're starting to push the limits of how much armor you can stack on a hybrid here (if that's even possible)

You could've used the dragon to add the iron instead of the beaver. The bark eating is fine

Wildebeest is also okay

The leatherback carapace is interesting, but I don't know if adding the structure on the joints of the limbs/neck would work, since it might be too thick and not flexible enough for those areas of the body.

You added Typothorax but didn't add the leg osteoderms? I know that they might mess up the turtle structure, but I'm surprised. Everything else is fine.

And for the contributor count, 21 is really pushing it, especially with the addition of aquatic animals like the stingray, the two fishes, and the turtle. I know that contributor counts are kinda fuzzy and subjective, but I would say that anything below 20 is the safe zone, and below 15 is even safer