I see the conversation has kind of concluded. But I’d like to add some info that might be useful anyway.
There is a little bit confusion about how nodes share traffic. The process is actually really simple. When the satellite selects nodes for upload, it first selects a set of 110 unique ip/24 subnets. Then within those subnets it selects a random node. So effectively, whether you run 1 node or 100, you get exactly the same amount of traffic total. Download selection is based on nodes that actually have pieces and since multiple nodes on the same IP can never have more than one piece of a segment because of how upload selection works, it’s essentially just dependent on how much data you store. So by extension you see exactly the same amount of download as well.
Running multiple nodes is therefor only useful when you want to share multiple HDD’s. But each node does need to be vetted individually. And when traffic is shared among multiple nodes, that vetting traffic is cut in half per node as well, making vetting 2 nodes take 2 times as long. This is why you’re advised to start 1 node at a time.
I used to advise people to start the second node only when the first one is starting to fill up. But I’ve revised that a little since. Starting the second node when the first one is fully vetted on all satellites has the advantage of having a node that could take over traffic if the first one fails, without having to go through vetting. So there is an argument to be made for starting the second node after vetting is done on the first. For anything beyond that I would in fact wait until at least 75% of available space is used.
You mentioned you have 4TB HDD’s available. After a year of running my node it has broken 10TB only recently, got close to 11TB but is now dropping down again. Most likely that 8TB for the first 2 nodes will last you a long time. So don’t even worry about starting more until it becomes an issue.
One last note: Because traffic is split among nodes, the load on each individual HDD is halved as well. Because of this you most likely don’t need to worry about SATA II if you’re running multiple nodes. So as long as you have the ports to connect the HDD’s, I wouldn’t spend any additional money on controllers.
This goes for other resources as well to a certain extent. There will of course be some overhead for each individual node process, but for the most part resource use per node will drop when you run more than one. Therefor I think your hardware should be able to run 4 nodes. Just don’t go overboard on the number of nodes, as there will be no advantage of doing that. Add one HDD & node at a time and you’ll probably have a pretty good idea on whether your hardware can handle an additional node.
Hope that helps!