Hello @zeiz and welcome to the forum 
Your configuration is okay performance wise for Storj I think.
Be sure they are statically mounted via fstab.
Wired network is the best option.
I believe 100Mbps is currently fast enough for Storj.
The best approach is usually to have one node per HDD as suggested by @nerdatwork.
You’ll need one authorization token (aka EDIT: to then create and sign an identity) per node.
So to start things off, one identity would be enough to spin up your first node.
I would choose the disk that consumes the less energy to begin with, to be as energy efficient as possible.
When this first node is nearly full (say 90%), you’ll be ready to start a new one, with a new identity and new HDD.
It highly depends on how much power the whole machine draws, and electricity prices in your country.
New nodes take many months before making a bit of revenue.
Have a look there, copy this spreadsheet to your own Google account and fill in your numbers to have a rough idea of what you could expect: