U can cut the long branches severely, they will branch usually from the nodes that are left at the tips.
I cant really tell u what season its best to do this, but i guess any time will be ok in your zone.
For training i actually do not prune mine, i just tip the new growth once it has 3-4 sets of leaves, that keeps them more compact and denser. I do do this becouse i have to, mine have to be very compact ,both the ones in the greenhouse and the potted ones. U have way more space there so can let it get bigger as u dont have to take them inside for winter, or fit them tight in a gh, like i have to.
U can use the pinched tips for tea, also the leaves, so i have red.