most if not all hub motors spoke holes are 2.3 or 2.6mm
So, just like most normal hubs then🙂
I'd probably use DT Alpine III or the like for anything load bearing, they're 2.3mm at the head/bend, which is about a third more cross sectional area than 2mm spokes.
+lynx most if not all hub motors spoke holes are 2.3 or 2.6mm IIRC so you'll require the washers.
Would have gone for 13 or 12 gauge spokes but that'll be a custom order which will be spendy, so washers it is.