It might be related to the mesh itself needing to be the root, he glazed over it in the beginning of the tutorial but it is immensely imperative. You had it right, just dragging it over the root and dropping it.
Now we can get into some debugging! So first things first, is the pawn set to auto possess when you start the game or do you have it set as your default pawn in your gamemode so you automatically spawn as it? Otherwise you spawn as a totally different placeholder pawn.
If you put some prints on your character’s inputs just to verify it’s receiving them, it might clarify some of the issues!
Also, for the spline bit, it’s more relevant if you were doing older starfox titles where you were on rails and only moved around in the screen space. That tutorial just gets you the spline movement, after that you’d still have to add local offsets to the ship to move around the screen, and even more work to aim things etc. It’s just the first piece to that puzzle. F Zero X was kind of the same way. Constrained to the track without full 3D control. Many things we do tend to start as one thing and add different bits of knowledge (and usually kitbashing tutorials together in the early days) to get a different outcome.