I just think four is a good number. Doesn't seem like too little, doesn't seem like too many, and gives some good variety.

For Thero, I like Tyranno, Velociraptor, and Spinosaurus as all three feel pretty distinct to me. But (and this is an honest question) what does Allosaurus bring to the table that the T-Rex doesn't? I'm tempted to lean toward Carnotaurus just because it's got horns, making it a little more special.

I thought the idea is that all of the Theropod/Thero form dinos would have flame themed attacks/undertones.

oh no worries there in my head i can see the flaming kicks slashes and punches now XD

Three great minds think alike.
T. Rex: strength
Velociraptor: speed
Spinosaurus: blade attack
Carnotaurus or Allosaurus: flame attack

Allosaurus has horns too, just throwing that out there.

Meh im okaywith either one honestly because last i had heard a Carnotaurus hadnt been used in sentai or Kamen Rider before so I thought it could be a nice change of pace XD oh well popular vote wins either way am I right?

We can use Carnotaurus if you want, I just thought Allosaurus is easier to pronounce. (:

I'm gonna offer some slight tweaks:

T-Rex: Strength. But maybe a focus on kicking and leg strength. The special attack could be a low powered Rider Kick. (as opposed to the form finisher being a combined four dino flame barrage kick.)
Velociraptor: Super speed, with the addition of claw weapons. The special attack can be a fury swipes quick and deadly slash sort of thing.
Spinosaurus: Adds a blade weapon. The special attack could be just a typical badass sword power-up finisher.
Carnotaurus: I'm warming up to the idea of a primarily focused fire mode, just so that it gives him a bit of ranged capability. But only if the other forms have a similar "pure" elemental mode. Maybe in this mode he focuses on punches and things as opposed to Tyrannos kicks. The special attack could be a big 'ol fire punch. I only choose Carnotarus over Allosaurus because of the more prominent horns and shorter snout. Not only does it just set it apart from Tyrannosaurus even more, but it just looks more heavy metal. Demonic maybe. Adding to the fire based theme of the mode. :p

Let's make T Rex give him strength throughout.

Velociraptor should just be speed.

Spinosaurus could be energy blades, not real blades. This is just Dino DNA not real weapons.

Carnotaurus could be like Max Flare, just surround his arms with fire or something.

For the rest of the dinosaur power ups that give him weapons, keep them at energy constructs, not real claws or weapons.

Each form has only one finisher. Each power up doesn't get its own finisher. In the finishers, all power ups activate at once. So for therapods, it would be Paleo doing a rider kick super fast with a strong impact, on fire, and with energy blades.

Why are you just deciding this stuff through and through without any other input? Yuu pretty much suggested from the start that by chomping the jaws twice, each power-up would provide an attack function. Now all of a sudden that's changing for no other reason other than because you said so?

Yes. Tyrannosaurus would be strength throughout. There was no question there. I just think it would make sense if the fighting style changed a little given the fact that T-Rex are so... leggy. Likewise, the fiery arms of Carnotaurus promotes more of a punch focused fighting style.
Keeping in the spirit of modern Kamen Rider, I don't think "energy blades" is very likely, realistically. Yes, I get it. We're not selling toys here, but if it were a real show, you know they'd have to. I still think Spinosaurus should give him a simple sword weapon like the Daidaimaru. If he has a all-form encompassing sword weapon too, that mode has him dual wielding.
Velociraptor doesn't need physical claws, but I do think the attacks in that mode should be slashes. Like he zips past and around enemies sideswiping them over and over.

I agree with Rollout. Helios, you've been making a few decisions without actually asking. As for it just being DNA, the DNA is just the catalyst to everything. The rest technology. So, yes we can have real blades and stuff. And actually since we are using DNA, the suit could grow claws and whatnot. Using the DNA as a catalyst opens many doors.

I always liked the idea of Raptor as the base form, save Rexy for Final.