Had a quick look at your diagram. What kind of links are between the routers in Area 0? Are they point-to-point links as the diagram suggests? Or are they some kind of WAN 'cloud'?. I'm not sure how your central routing can work with all your core routers apparently on the same IP network
Yes they are point to point links.
The routers are infact Linux PC's acting as routers.
It is all for a computer laboratory.... simulating supernetting concepts etc. But I need the host PC's to be able to demonstrate the whole concept etc.
Hmm, I don't want you to change your whole network or anything but wouldn't it be wiser to use a 30 bit mask rather than the 25 and 28 bit masks you have for those point-to-points? That would give you two host IPs plus the network address and broadcast address for each point-to-point link and they would be on their own separate subnetwork.
Now assigning a network address to your LAN segment depends on how many PCs will be connected into it. So I would assign something like 10.0.0.0/29 to your LAN segments if you have more than two connected to each router. Regardless I would calculate the LAN addresses first, and then finish off with the point-to-point links.
Doing it that way will better utilize route summarization I think.