For one or maybe two fish I use the old manual filet knife. If I have a bunch of fish (or large fish) I use the the electric then finish up with the manual knife to get the last bit of meat of the bones,
As for sharpening, about 5 years ago I was having trouble keeping my knives sharp, stopped by a local commercial knife store and talked with the tech. He suggested the: "LANSKY FOUR ROD KNIFE SHARPENER", (UPC 080999081006) about $20.
Best knife sharpener I have ever used, and really simple to use...I threw all my other sharpeners away.
That's my 2 cents worth.....

Bruce 10982 here are my thoughts:
Get the Lansky sharpening system. (I use the five stone kit) it retails for $58. Follow their instructions. To best understand what you are doing when you sharpen a knife read, “The Razor Edge Book of Sharpening” See the video: https://www.fishermansprocessing.com/videos.php on how a West coast fish processing house processes a #200 tuna. I doubt that the fish you are filleting is much bigger than the last steak you ate. Even if it is, any 6” fillet knife by Rapala, Buck or any others would service you very well. The need to use an electric knife is completely lost on me. I spent some time watching a variety of internet videos showing how to fillet a fish. The process is basically the same one the deck hands use to clean around 150+ fish on a ½ day boat trip. Start with the cut behind the pectoral fin down to the spine and turn the knife 90 degrees and run the blade down the spine and voila you have your fillet.

I hope this helps.

One of the many things I need improvement on is the art of fileting. I'm getting better with experience but most of my fishing is catch & release. I only keep what we eat. Something I have instilled in my grandsons. I use a 6" Rapala filet knife that i struggle with to keep sharp. I use a ceramic steel on it but it just doesn't keep its edge. To make a long story short, I see a lot of You Tube videos where these guys are just whipping through all different type of fish making perfect filets with electric knives. They make it look so easy. I'm open to suggestions, as I have always said I am a student of this sport. Thanks in advance. You folks have been great to me.