While it's likely the one wearing Kouya will be the muscle of the team, I feel like this character could be the unexpected tanky and heavy defense type looking at what I assume is a shield on the back of the armor.
As for voices, a comment on Reddit suggests that Ayumu Murase may voice the Suiren wearer and Junya Enoki may voice the Soukyuu wearer, which, judging by the initials that were revealed and tone of the voices, seem very likely. My guess for Kouya and Senkou at the moment are, respectively, Shunsuke Takeuchi and Kentaro Kumagai.

Suiren's definitely keeping his predecessor's versatility - hopefully he'll use it more too. The shield is an interesting touch, I hope it's not another case of the water character being relegated to a defensive/support role, and it's definitely something different. Not really a fan of him using a short sword instead of a spear but then my bias is legendary. What really catches my eye is that the claw on Suiko's right arm seems to have been replaced by what looks like a hook.

https://i.postimg.cc/GpPGJN86/CDK-rajura-web1.jpg
https://i.postimg.cc/FRDSwLxZ/CDK-rajura-web4.jpg
https://i.postimg.cc/j22fTSgr/CDK-rajura-web7.jpg

Oh that's the stuff right there.

Apparently a bunch of design docs got leaked earlier this week and if any of what I'm hearing is true, things are... taking a very interesting turn.

https://www.youtube.com/watch?v=mJ5dOSMYhtM

Names revealed
Gai of the Scorching Heat
Kaito of the Blue Sky
Musashi of the Waterfall
Yamato of the Wildlands
Shion of the Flash

Musashi definitely sounds like our beloved Don Murasame, Ayumu Murase.

Which lines up with some of the material leaked last week...

Also:

https://i.imgur.com/zdZFOLb.jpg
https://i.imgur.com/bQMtyI3.jpg
I freaking called that it would be a 30M base.

Yeah, which has me wondering if their fantasy lineup under 30M and FrS were testbeds/ways to rack up know-how for stuff like this.
Also, Musashi and Yamato seem to share the same last name, Hojo. So, maybe they're brothers or cousins?

It's something I'd been wondering about for a while actually. It's definitely a much more affordable alternative for gimmick-heavy lines than, say, SHF, and a nice middle ground between that and basic Rider/Sentai figures.

Adopted, as it turns out! Friend of mine did a rough translation of the blurbs on the official site.

Gai of the Shakunetsu armor
name: Gai
voice: Ishibashi Hiiro
about: 14 years old. He was found to have the qualities to be a samurai trooper, and so he wears the Shakunetsu armor and fights against the youja. His sense of taste is different from ordinary people and he prefers something unusual.

Kaito of the Soukyuu armor
name: Uesugi Kaito
voice: Enoki Junya
about: 15 years old. Raised by his grandmother, Uesugi Yoshie. While he has an interest in rock music due to her influence, actually he also has a hidden hobby. He fights the youja wearing the Soukyuu armor.

Musashi of the Suiren armor
name: Houjou Musashi
voice: Murase Ayumu
about: 14 years old. He grew up in the orphanage "Forest of Truth." His ability as a samurai trooper was recognized and he became Musashi of the Suiren armor. He checks fortune telling daily on his phone and believes in that advice and lucky charms.

Yamato of the Kouya armor
name: Houjou Yamato
voice: Takeuchi Shunsuke
about: 16 years old. He is from the orphanage "Forest of Truth" and is like an older brother to Musashi. He has admiration for heroes and his sense of justice is stronger than anyone else. He's the one that supports the other members by lifting everyone's spirits. He fights wearing the Kouya armor.

Shion of the Senkou armor
name: Ishida Shion
voice: Kumagai Kentaro
about: 18 years old. A long-haired young man who often uses English words in conversations. Contrary to his appearance, he is compassionate and cares for his friends. He wears the Senkou armor and as the oldest he leads the other members.

Nice. :rock: And looks like I was right about Yamato and Shion's VAs.
So far, Gai looks to be this team's loose cannon, Kaito the voice of reason, Musashi and Yamato look to be the Mone and Aguri of the team, and Shion the tsundere big bro.

Well... remember those leaks I mentioned?

(Spoilers ahead in ROT13)
Nccneragyl gurl'er tbaan chyy n Zvxr/Nyrk jvgu Fuvba nf gur Yrb/Jrf

Anyway neat little tidbit from the discord group: Nasutei/Mia's mansion was in Odawara, which is, historically, the territory of the Hojo clan.

The same clan for which Musashi and Yamato are named.