More defoliation? When?

Three weeks in flower, one of noticable stretch, she's really thickening as well. Should ya wait for some bud development or defoliate early in stretch?
By a percentage, how much can safely be removed?

Pretty even canopy so far. I would wait to cull out the lower junk

She looks fine, let her carry on. all those leaves are very important. they are absorbing light and allowing the plant to grow bigger buds

I typically don’t touch my plants after the 2nd week personally. Can’t promise there won’t be any slight stress to the plant, but if you do decide to defoil and remove pop corns, make sure to do it in stages and not all at once to lessen the chances of stressing her too much.