But if you can get your hands on the manga that I mentioned earlier it'll make more sense and feel more complete as a whole.
Huh... no. Things won't "make sense". The fully scanned manga was posted on 4chan's /m/ board a while back, although I don't know if they were stored anywhere.
In any case, it won't make sense or make anything feel more complete because the manga (and the original script, if the manga was really closer to it) doesn't line up with how the series actually turned out.
Basically, the plot hook of the show mentioned in the first episode, the fusion of the worlds, seemingly had already been resolved by the time that All Riders' story started originally, so the manga doesn't solve people's main problem with Decade, the resolution of the fusion of worlds story given by Movie Wars 2010.
The All Riders movie that we got had basically the same story as the manga, only with some stuff tweaked to make it fit before the resolution of the "fusion of worlds" story (like Eijiro surviving, the fusion of worlds continuing and the brief mention of Tsukasa's real journey not having started yet) and to promote Double.
Aside from that, the manga keeps most of the revelations of the All Riders movie, like Decade as the Great Leader and such. The manga does have a few neat touches, like starting with another one of Natsumi's dreams rather than the Amazon battle, and one main advantage compared to the actual movie though - no Double stealing the Shadow Moon battle, but, aside from that, the differences are just minor details and different Rider/monster cameos. The overall flow of the story is the same.