I am not sure how much to answer here. Some of this seems basic but in some ways you seem to have hit some points that really need a deeper explanation. I am not even sure your book is going to answer all this but let's hope it does.
For a given power out then things are fairly simple. A low voltage winding needs thick wire to give high current. If you work at high voltage you need a lower current for the same power so you need thin wire. Things work out that if you double the volts you need double the turns and half the current. This means that you halve the wire csa and everything works out fine. The winding takes up the same space although you have more turns.
"And for the magnets, I see many posts with info about rewiring stators with thicker or more turns but nothing is said about the magnet size or strength. Also when I look at some of the completed units, the magnet does not seem to be large enough for the entire coil to be in the focused field, is that an efficiency loss? "
This is a deeper matter and I have good reason to understand what is puzzling you. There is much discussion here about wire size and number of turns and some of it is not helpful, it no doubt confuses you and to be honest I doubt that it helps the person asking the question.
Alternators for wind power have to be designed as a unit and unless the magnets, windings and blade size are all chosen to match the thing will work badly.
There is no point in worrying about what size wire to use or how many turns to use unless you have settled the other issues. For a given magnet set up and blade size there is no virtue in changing turns, wire size or winding multiple strands in hand to alter an existing design.
I believe many are convinced that turns and wire size are the only things to consider.
I will stop at this point until you have got your book. When you get your book, read it through and some of this will be answered. Come back and ask the questions that you still can't follow.
Flux
