In a perfect world, mistakes aren't made. In reality they are the best teachers around. Trying not to make a mistake makes you too cautious. Waiting to see every practice done in front of you will slow you down. TRY things. Get trees that may have a bit of promise, as well as some that have more than a bit. So what if the tree is weakened or killed, if it taught you something...I've been there as well. Doing things like this have taught me a fair amount, but I'm tired of just feeling around to learn what I need to do. For instance, I've hacked some roots of a tree when repotting, and although it lived, I set the tree back at least a year by weakening it too much. That's a frustrating feeling. Of course even very experienced people make mistakes, so I know I'll never not make mistakes in this hobby. BUT, I'd rather be shown certain techniques applied correctly so I don't keep making mistakes that set me back.
That's what we old timers did back in the day...look at a book, take a whack at the tree. see what happens, kill the tree. Price of experience.
Also, find a DECENT bonsai place within two hours of your house if possible. Go there for individual lessons. Also, get an extremely expensive (within reason of course, think of your top price you'd pay then add $500 onto it) Thing about an expensive tree is that you will be forced to learn things to keep it from dying--which is extremely important if you're married. Nothing like having your spouse ask what you paid for that dead tree...It's a motivator.