A second stator and 3rd rotor are less effective than using all the material on 2 rotors and 1 stator. Of course it can get pretty big with magnets that size.
"So what kind of effect will the aluminum wire have?"
Soldering aluminum is difficult (an understatement).
Kester used to make a special solder, with a special flux core, just for AL. I have not seen it for years.
With so much wire going to AL, it would be nice if they made it available again.
Look for older microwaves. The older the better.
Much larger transformers and copper windings.
"Should my coils be wound similar in shape to the magnets?"
Yes. The hole can be a little smaller than the magnet to squeeze a few more turns in.
"What voltage should i go with?" & "i would like to occasionally charge batteries"
Then 12V.
"though I'm not sure how i would want to turn it yet"
It is simpler and easier to get power out of a HAWT, especially if small.
It would be a good idea to try to define how you want to turn it, and the 'size' of everything before going much further.
G-