Occams Hacksaw
Seedling
Bonsai from seed sounds like it's easy to do. It's not! When you grow young stock, you want to develop low branches, taper, short internodes...
But how do you do that? If you're a beginner, you won't know how! By the time you learn enough to know how, the seedlings have outgrown the stage where you could have set them on a good course. Meanwhile, the seedlings you have spent years growing a pretty much useless!
The best way to learn bonsai is to start with a larger plant, and cut back. Then let it grow out again. Once you learn how the plant responds, then you'll have an idea of how to grow from seed.
I'm a beginner with bonsai, but not horticulture. I have experience training container plants with guy wires, clipping, pinching, and combating/preventing pests. It's been a hobby of mine for years. I'm just not used to growing things in a drip tray. I am pretty good at moving growth around and keeping plants (and especially their roots) healthy. I enjoy taming plants. That's how you get the most out of them in my experience. That same experience knows that the sooner you start, the better your results. I often start training plants after the 3rd set of leaves depending on the plant and how I want to fill the space with it. I'm expecting that a large amount of my experience will translate well into bonsai.
That being said, I agree and I do fear early critical mistakes/missed opportunities on a plant that you keep around for so long, but I have faith in the community here and intend on showing my progress and asking for advice. According to my research on maples, I prefer a clip and grow method of styling the trunk. I also look forward to early influence of the nebari. My research on other trees and their likes are fuzzy at best. It gets overwhelming fast and I had concern over my original choice of Red Maple, as much as I'd like to do it. With every ones help, though, I'm building a nice list of appropriate trees for my area that work well for bonsai.
Also, yes, I intend on slapping some around in the meantime and I will keep your warning in mind. But if I get 5% of my seeds where I want them, I'll call it a success given it was my first try. I'll also learn a lot.