if you use a trellis for only support, you still have time.. figure about half way up the future vertical growth is good for support. If used to help train the plant horizontally, put it on now or even before this point in future grows.
Defoliation is not wise. Selectively pruning is fine. Always have a reason to remove a leaf. They do several important things for the plant - light absorption, molecule production/building, and they are the lungs. So, if you dont want to reduce the limiting factor of CO2 intake, don't blindly remove a bunch of leaves thinking it helps.... There''s a chance you delay flower due to the stress of it, too.
Read "to defoliate or not..." on cocoforcannabis.com. the guides and posts in dr photons corner will help you avoid numerous urban myths/bro-science nonsense.