From what I understand, just an amateur, these giant stars tend to form in denser dust clouds. I do not know the time it takes to form compared to out ordinary Sun but given the higher density of the dust gravity takes over and I do not believe one is talking about a big difference but as I said this is pure conjecture on my part.
You are correct. Also note that there are practical upper limits to the masses of stars. A star with too much material in it may never become stable. The effect of convection will be so great that a fairly fixed surface may not be able to form. Look up Eta Carinae for an example.