Hello @kommie1949 and welcome!
One tool you can checkout to estimate how long it’s gonna take to fill up space is this community-made estimator:
All nodes behind a /24 subnet are all considered as one. Which means that if you’ve got 1 node behind IP a.b.c.d getting 4GB/day (e.g.), adding 1 another node as a.b.c.(d+1) would split the traffic between the two (that is 2GB/day each). Overall, you wouldn’t get anymore data.
On the other hand, if you’re able to run each node on a different /24 subnet, then you’re very lucky and each one would get full ingress traffic.
I reckon adding more nodes in different /24 subnets wouldn’t really impact your other nodes traffic wise, unless you add like hundreds of nodes…