Yep it’s fun, but especially when you factor in you own time, it’s not a cost saving exercise 
I would buy this in paperback:
Depending on what you’re building you’ll get different challenges, crown race setting and bottom brackets you might want to outsource to your LBS.
Also, come race day if your shifters disintegrate with 30km to go, you’ve only got one person to blame… 
But seriously it’s great knowing everything about your bike, particularly if you have to take it apart and travel to races and rebuild it. When things go wrong, you’ve got a much better chance of anticipating it and coping with it. 