crawl space insulation for zone 7a (south carolina) - r-value and faced/unfaced?

Replacing damaged insulation in my crawl space, which will make contact with the subfloor. Original insulation was faced, but can't read anything that used to be on it.

Google seems to suggest R30 for subfloor contact, but wanted to confirm. Seems like my options locally are owens-corning and knauf.

Is there a big difference in faced/unfaced for this application? Just whether my hands get itchy?

Lastly, are the wire hangers that come in the 100-packs recommended for this usage? I don't have a pneumatic staple gun anymore but I suppose that only matters with faced insulation anyway.