As it goes with most things, the answer is...it depends.
What are you looking to get?
A super nice custom frame? Your Yamaguchi school frame will be much nicer than anything you'll produce the first time around.
DIY pride? There is a lot to be said for going it alone. Soemone said in another thread here that the process itself can be very rewarding- and I agree with that.

My story (condensed version): I started building frames because I'm the type who has to be building something and I wanted a bike that was only available as a custom. I built my first four frames/forks with no jigs or outside help beyond the info I found on the internet. It was the harder way to go for sure, but it was right for me. Later, when I worked in the shops of a couple of established pros, I found I had the base knowledge that let me quickly take my framebuilding to the next level.

All that said, only you can decide whats best for you. I knew that I could figure it out and make it work, so I went ahead and built a frame.

I hope that helps!