Efficiency is not going to be your problem, matching the load is.

With those magnets you need discs of about 30". If you squeeze it down to 24" then you would make better use of 20 poles.

If you design for a low wind cut in the thing will go completely into stall with a 5M prop. If you optimise for higher wind cut in you can get extremely good efficiency around 20 MPH.

I have no idea what size prop you intend to use, you have better ideas of what you can manage but you will easily get the 5kW with 5M if you match it right but you are going to have to do something cunning to work over any significant speed range.

My choice would be to match direct at about 16 mph and use a boost converter for the lower winds, but if you want to do it without converters you will probably have to compromise with a cut in around 10mph and use large heaters in the dc line to keep the prop speed up. This will reduce your battery charging efficiency in high winds and will be ok if you can use the heat, if not it may be a nuisance.

Perfect candidate for Nando's mppt tracker if you can live with electronics.

3. 34" between them i thought that a double layer winding would give me more poles hence more voltage i do realize the insulating needs to be well between phases
85. volts is right i only put 120 volts as a desired voltage.

If you make a big powerful generator with low resistance it will run at virtually constant speed and you want the speed to rise with the wind to keep your prop from stalling.  

For small machines the standard procedure is to choose just enough magnets to make an alternator with the desired resistance, this is the cheap option and is fine as long as you can dissipate the heat produced in the resistance of the stator.

With bigger machines it becomes more difficult to get rid of this heat and in the case under discussion he has chosen very large magnets. the internal resistance will be too low to avoid stall. If is better but more expensive to have the resistive loss outside the winding as it doesn't heat the stator. It is ultimately a trade off between magnet cost and what power you can safely loose in the stator. As you  say " it depends on how much you can spend on magnets".

This is why the mppt schemes with voltage converters can extract more power, they match by letting the volts rise and you can reclaim this power lost in heat.