Bicycle hub dynamo - zero drag without load

[PMoi]

I'm interested to build hub dynamo for my bicycle trailer. Axial flux generator design (for my knowledge) don't generate extra drag when unloaded.
I would like to charge various mobile devices from this generator, so basic power aim is to have ca. 5V and 1A output from it.
Plan is to have dual rotor design and coils between.
Speed target is about 230prm (20" wheel@25km/h) for 'nominal' output. I have neo (N42?) magnets which are 25 diameter and 6mm tall which I'm could use for this.

Any quick rule of thumb advises about feasibility of design?

Is 3coils/4magnet poles enough or is more needed?
(6/8)?
(9/12)?

I would like to learn some comments before starting to build test setup(s)

[electrondady1]

the tricky bit is supporting the stator within the two rotating mag disks.
 

[PMoi]

Thanks for this comment. I believe that I get this part of structure sorted.

I would like to get some comments regarding power output vs magnets required.

[electrondady1]

other power has members that can calculate how many turns you need just from how many lines of flux your crossing but sadly , i am not on of those. if your only looking for 5 volts and 1 amp, at 250 rpm it's quite a different  device from a windmill alternator. you won't need many turns of copper in your coils . set up a steel rotor with mags and do a test coil. even though it is a temporary set up for testing , at  250 rpm you will want something to keep the magnets in place.