I connect multiple OVO Home. The total land area is actually more than 70X40 anyway.
As to ventilation, they thermoventilate themselves. If too cold they snuggle together to sleep. If too hot they sleep in the OVO den, with sand & shredded tissue as a nest.
Also they like plugging the ventilation holes themselves with bedding. Go figure!
I actually was very concerned about ventilation too until they started plugging the ventilation holes themselves!
Pls see below picture. When I was using Carefresh all the ventilation holes were solidly plugged to my amazement!
Now I changed to compressed wood pellets. They tried again but failed coz the wood pellets roll down! Hamster 0 Ventilation 1