There are a lot of very good, build them yourself modulars today as well, such as the MOTM and such. Also don't have to worry finding part for a while.

As for big manuals and such, it depends what you do. Physics in audio alone is enough to try and comprehend, let alone electronic attempts at emulating various things though various types of synthesis is another. Depending how far you want to go in understanding what is going on and what type of control you want over your instrument determines how deep into all of that you would like to go.

Depends on what floats your boat, but just like a guitar, if you want to master the instrument you have to study and practice. There is no way to make physics any easier to understand than it is. heck we still don't know how the human ear totally works.

With that in mind, there isn't anything wrong with know three chords and making great music with just that.

Creativity and the science of sound are two different topics. But for a synthesizer to offer exstensive controll and various synthesis options, such as a Kyma or a Kurzweil, then your gonna have a huge manual to explain how they implement Granular, FM, subtractive, or whatever else they offer. Before you make the most of them, your going have to have some idea how the pricipals work as well. Then your going need to apply them to something relativley standard like a two speaker stereo playback system. This can go on as much as you would like. Nothing a manufacturer can do to make the ideas simpler, they could just can make the UI managable.