Wheelbuilding / Wheel Building / Wheel build help

Need advise on parts choice, now have:
Zipp 303 firecrest tubular rim (285V4) 24h
American Classic Rear Track hub 24h 2.5mm spoke hole
Planning to order:
Sapim Super CX ray spoke
Sapim alu nipple 15G 12mm
and my questions are,

1. What is the real ERD of Zipp 303 firecrest tubular (285V4)? Zipp website said 555mm but wheelbuilder.com said 549mm, the 6mm off make 3mm spoke length difference in calculation.
   
2. The Sapim Super CX ray say in the description they should be used on hub hole size 2.3mm or less, will this cause a problem using them with 2.5mm hub holes?
   Thanks