No, you absolutely do not need an electric power planer. We recommend shaping your first few boards by hand with the tools included in the kit to understand what you're doing and have control over how much foam is removed. As soon as you put a power tool between you and the foam there's no telling what mistakes will happen as you're trying to get the hang of both the proper sculpting of foam as well as how to use the planer correctly on foam. Once you shape a board or two by hand and understand the process and how the shape comes along then you can use a planer to take some of the elbow grease out of it...
We do offer customization of your blank to take away most of the useless power planing to thickness. If you'd like we can provide your blank 1/4" thicker than your final shape thickness so you only have to scrub a total of 1/4" of foam (1/8" from deck and bottom) which is pretty quick with out rasps provided in the kit. If you want a custom blank thickness just put a note in the "custom blank specifications" section of the cart and we'll cut it the that thickness. No problem.