Saving power is a bit of a misnomer as the router’s power draw is negligible but you could try powering the router using a USB port on the TV/streaming box. I do this with my set-up using 2 USB ports and a dual (2 >1) USB cable.
HMA is pants - get yourself a decent VPN provider.
You only need about 5 Mbps to stream, so the MT300N-V2 should be fine.