Responding to myself...
Datasheet reports 7.05 idle watts (~11w at active random read) so depending on what it considers idle, it'd be 8*7.05|11= 56.4:88W
Server clocks in at ~102W. Halving the drives would reduce the power by 27 : 43%
And in theory other components (motherboard, CPU...) must be using anywhere from (102-88) :(102-56.4)= 14 : 45.6 W.
Correct.
With normal split tunneling you can normally do something like this anyways, but it can be finicky to configure, and easy for something like DNS, etc to access the internet without your VPN in the middle. And sometimes if your VPN fails to connect, you could be connecting without your VPN.
By using docker with gluetun + qbit (I believe docker images for this setup exist already) you can force it to use only your VPN, and if the connection fails then your bittorrent client can't connect. With gluetun all your bittorrent traffic would flow through your VPN, but there's a way it can be configured to allow only your webui port to be accessed locally on your network