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The KX250 manual has a general range for fasteners early in the manual... Honda has a similar spec early in their manuals, BUT a lower spec for the rear shock shaft nut... I know the Honda spec is for a Showa shock, and the KX250 has a KYB, but if it's an M12 nut, I'd use the lower torque.

25 ft-lbs should be sufficient. I would peen or lock it in some fashion.

I do it the way Last2Stroke's documentation shows. The oil cup isn't necessary, but it can help you avoid making a big mess. If you don't have the oil cup and you're working on a KYB shock, you can install the adjuster body far enough that the o-ring seals it up without installing the sleeve, the spring and the adjuster piston assembly. You just fill it up as shown in those instructions, screw the adjuster body into the shock body to cap off that hole. Stroke the shock a few times to get any remaining air out of the main-piston...

Think it’s just for filling so you don’t introduce many air bubbles. I don’t think it’s necessary either

It’s called a ……

Kawasaki's service manual shows filling through the shock body.. The oil cup is then used to bleed the air through the compression damper's bleed hole... The alternative method is to fill through the compression damper adjuster hole, and bleed before installing the compression damper... or you can fill through the shock body, remove the compression damper and bleed through the compression damper hole.

What’s an oil cup? Id say not necessary

Loctite AA330 is pretty awesome. Used with aerosol acetone as activator. Good for 120°, sticks super fast, 24 hour full cure apparently but I bond aluminium cable tie mounts to chassis / engines and I can cable tie wiring to it in 15 minutes.

Dualock