TO answer your question:
The eSI is called the SI over here, but they are slightly different (only a little) The eSI chassis is an EG5 and the Si is an EH3, same motor, but we are LHD with no side marker lights, and a small lisence plate "indent" in the rear.
If something is stock, it is OEM
Are you referring to the axle nut? I think that is a 28 or 30 mm socket. The brake disc doesn't bolt to the hub, it just slides over the lug studs and is held in place by the wheel.
Sorry to answer your message so late (if it even helps) I just joined.