Your not going to get a lot of good advise with this kind of question because its way too open ended and really a "rabbit hole"
But I just did this on a different bike and really wasn't too hard. Think of it this way, first make all your controls/lights run off the battery; lights, turn signals, brake switch and everything. A pure LED lighting system also helps because it minimizes battery current draw. Second, to keep the battery charged you will need to run the AC to a rectifier/regulator then to the battery. So the stator is wired in parallel to the Rectifier/regulator which is also wired in parallel to the battery. Grounding the battery to the frame wont hurt anything even if the ground is floating. Baja Designs or Trial Tech has all the parts. If you can get it all working just from the DC battery,then charging the battery when the motor is running is really easy. You will need some type of small battery no matter what