I use Handbrake and my own secret sauce preset with Tdarr. Hardware encoding is good but I prefer using CPU and squeezing the maximum quality and smallest size for h265. Tdarr is what you are looking for. All these questions have been asked and answered there.
Reminds me of that joke about looking for a quarter you dropped where the light is better even though you dropped it in the dark. What you need is a miracle. You have 3.5 inch drives and some SBC devices. How do you plan to hook them together without buying some hardware? Your options are slim and next to none as far as I can see. What kind of suggestions are you looking for?
you wouldn’t like it. I scale everything down to 576p. The result is small movie but there is def a loss of quality. I tuned it to the limit as far as trading file size and quality. 576p is actually standard definition but if done right the result looks like HD. At least to me.