At some point, you may eventually move to using power tools, especially if you plan to do full sized decoys. Knives, gouges, spokshaves, drawknives, surform rasps, rifflers, and files all have their place, but power does too.......
I am an oddball when it comes to "carving" decoys. I recognized, early on, that I was "sharpening challenged", but could strop. I, from that point on, used exacto #2 handles and #22 and #24 blades. You can also use the fatter xacto handle that holds the 2 series of blades, but I learned to carve on the skinny aluminum one, and it now feels natural to me. BUT it works for me because I use the knife only for some detail and cleanup. The majority of my carving on heads is done with a foredom (so I guess what I do is not carving, but "grinding"?). I can still carve a head from a blank in reasonable time with a knife, rasp and sandpaper; but I can do a better job in 1/3 the time using a foredom and knife. When carving a dozen decoys at a time, that saved time is a big thing to me.
If you can sharpen a knife well, and buy a knife following the advice of the duckboats members who use custom made carving knives, I am sure you'll love it. The first knife you learn on will become as natural to you as my goofy Xacto handle and blades are to me, and and it will be a useful tool in your arsenal, even if you move to power tools for some or most of your wood removal.
Mike