Let's see...

Long, back and forth motions on the limbs/back are fine. Do circular on joint points like knees, elbows.

Clockwise on abdomen. Clockwise or counter-clockwise on heart - feel the Chi and do what seems balancing. Some days for me it's a bit of both.

Really focus on your underarms, there's a busy nerve nexus there. If you only have time for a quick brush, go for under the arms.

Convenience is key! Healthy habits should fit into your lifestyle, don't worry too much about showering or not or when, just DO what you wish to do. :) It's important to do things in a way that makes you happy. If you resent it, the healing power is lessened. Remember the placebo effect? It's like that.

Always avoid skin eruptions, don't brush there.

Yes, you can wash the brush, I just flip it about a bit to get the dust off.

Hope that answers your questions! :)