Ultimately it will be the turbine that determines what you get out, you need to establish the power out and speed of the turbine before you can settle much with the alternator. Speed ( or the lack of it) is a killer with a VAWT. Low speed alternators are large and costly compared with faster ones.
Having settled that, the output depends mostly on quantity of magnet, quantity of copper and speed.
Best you can do is manipuate the comparative costs of magnet and copper by playing with the design. The approach with neo may not be the same as for ferrite magnets.
Typically coils should be shaped to the magnets, round coils for round magnets, rectangular or oval coils for rectangular magnets.
The hole in the coil needs to be near or a bit less than the magnet size and the coils can touch on the outside. A good compromise is with magnets spaced about one magnet width at the inner radius for neo. For ferrite the more magnet you squeeze in the more you will get out but it doesn't use magnet efficiently ( with cheap ferrite magnets this doesn't matter but with the cost of neo you need to use them well).
There is no perfect geometry, everything is a compromise but you would do well to stick to what others have done over the years, it may not be perfect but it will work. There is so much information on the Otherpower site and Hugh Piggott's site that it really is foolish to start re-inventing the wheel.
Basic text book ideas will most likely lead you astray with axial alternators.
Flux
