1a) It's a good general textbook. You'll want to read other books on mundane astrology, if only so you don't sound like a parrot, and some reading in astrology in general is also a good idea -- I don't think I'd recommend trying to make a living as any kind of astrologer, for example, if you can't at least interpret your own natal chart.

1b) That's a very good way to learn it.

2) Don't obsess about it -- just decide, and do it. Flip a coin if you have to. That you choose is more important than what you choose. Me? I decide on a mixture of what interests me at the moment, what publishers seem to want, and sheer random whim.