Is washing with my hands enough, or do I need a brush?

You do not need a brush to make cleansing effective. More mechanical friction can be especially unhelpful when the skin is already reactive, inflamed, or prone to post-inflammatory marks.

Your hands are usually enough

Gentle fingertips and a suitable cleanser are a good starting point. If a tool leaves your skin red or uncomfortable, I would remove that extra friction rather than assume a stronger sensation means cleaner skin.