How long does the cushioning hold up with regular use?

Depends on frequency and storage. Keep it dry and avoid prolonged pressure when not in use. Most users get solid wear out of one pad over a season of regular work before noticeable compression sets in.

Can I wash this to keep it clean?

Yes. Rinse with soap and water, let it air dry completely before storing. Avoid harsh solvents or excessive heat.

Will one pad be enough or should I grab a pair?

One pad covers one knee. If you're doing extended undercar work, a pair gives you even weight distribution and less strain on each leg—worth the extra pad.