My idea is:
1: Get this plugin
viewtopic.php?f=73&t=7591&p=180230&hili ... ts#p180230
It allows you to cover the whole map with each service using only thing (sandbox only)
2: Make the city on sandbox, set demands up to max.
(optional, make a private plugin with loads of residents spaces, and spam it)
3: Spam the highest residential with highest residential map.
4: If you have diamonds or on PC, place tunnels on every piece of the map.
If not, just use normal roads, I recommend using the Automatic Water Pipes plugin