While I love zombies and KR, there's a few suggestions I would like to make, hopefully they will help you get some more inspiration:
1) If you're going for a more survivor-horror theme for the roleplay, then I would suggest emphasizing some common characteristics in those games. Namely, lack of resources and a type of claustrophobia to emphasize the need for survival without always the means to do so.
While I know that you are planning out other weaknesses for the rider suits, the existing limitation for 6 hours of use isn't enough of a limitation given that riders in the series hardly ever fight for that long in a day. Furthermore, what's to prevent these kids armed with these incredibly powerful suits from just escaping the area on their own?
2) The other point is the premise of the story. What were the soldiers sent in originally to do if a cure was being developed already? I can see that they could be sent in to "thin out" the crowd a bit before the zombie hordes overcome whatever other containment measures were put in place, but I don't find the idea of killing people that could eventually be saved very heroic unless we're making this a story of a choice between 2 evils.
An example on how this setting might be laid out might be that the government has this area heavily quarantined because of its high zombie concentration and several points of interest located within it. The soldiers and rider gears were sent in to perform specific tasks vital to creating a cure (e.g. search and rescue, intelligence gathering, retrieval, etc.), but obviously they were overwhelmed. Now, with the rider gears lost to a bunch of kids, these untested heroes must convince the government that they can complete the mission and stay alive. Otherwise, the military will have no choice but to level the entire area to combat the undead.
Whatever you decide, happy RP'ing.
