Turbo is pointless if you don't have a good router and devices that can support the speed, so don't get too depressed about it.
It will be until July 2019, as some have said, so you might need to wait. Are you even eligible for 300Mbps? If you can't wait, better to go for the new plans which is 100Mbps.
Up to you. You can, but won't make a difference.