I think people who are having the profit will say " sell " and people who are just buying Bitcoin at this moment will say "hodl". So it's depending on the view of each person.
Emm, yes. By sell bitcoin its mean we open new chance to grow the amount of bitcoin. But we must do it with right strategy and throw away our fear and greed, this is our enemy. But try to improove our skill in earning bitcoin is needed, so I will say that we have to keep buy and bitcoin in exchange, I mean trading.
This depends. When you're with bitcoin, you must hold it to be successful. When you're with altcoins, you can either hold them or sell them to buyers. Altcoins are creating a risk factor nowadays and I don't see them positively.