So with 9.25 mm you have the option of both 27 and 22 outer diameter bearings. Meaning you can use standard skate wheels(22mm od bearings) as well as the larger mtb hubs (mbs, trampa etc)(27mm od bearings)
Also. 9.255 or whatever is just a bullshit number made up to make it harder to find bearings. They’re just R6 standard bearings. Though the outer diameter will fit a little more snug than metric ones into your hubs. But they will fit.
12mm inner, 22mm outer bearings do exist but at like $8 each last I checked. Not to mention the small ball bearings will quickly disintegrate.
Mounts should be same as they depend on hanger not axles.