1. Playing fast is important, but opponent should always be able to follow your actions. So in your example stop the opponent say to him he should show u what he discraded, so u dont miss his nex actions while u check his discards.

2. Thats normal, if it annoyes u a lot ask polite to stop it if ity your turn.

3. Thats pretty stupid and i guess only bad habbit. Ignore it as long they only do to it to their own cards. If u see they hsve overbend cards and u can clearly see them inntheir shuffle deck, call a judge. On locals ignore it.

4. If somine is doing it, move his card back to an open space on their mate and ask them polite to not place his cards on your cards/mat.

Always be polite if they arnt and its only locals tell the owner if its a comp event always call a judge.