For all of your new questions the answer is mostly that it doesn't matter.
I would add the T closer to the ground, not up in the air, but not right near the ground either. But it really doesn't matter.
If the booster pump has connections for the same size PVC you are already using then there is no need for fittings or changing the size. Some people find the flexible hose easier to work with, but again it doesn't matter.
A shutoff valve might prove useful someday, but they are not always installed and it would hardly ever be used. Again, add one or don't as suits your tastes.