You can top as much as you want!
As long as you keep your plant nice and healthy it will survive A LOT of clipping. Your plants look nice so you can do it!
If you look in my grow journal (in my signature) the 2 larger plants have been topped 3 times now and growing strong.
I love topping and pruning my plants! I try to get them clipped and trimmed to fill out my grow space evenly. Sometimes the plants can get away from you though, especially during flowering. I try not to clip during flower but sometimes I have to because I would rather the plant get all the light it needs to in the right areas.
Sometimes you have to suck it up and sacrifice part of the plant so that the rest of it will thrive.
Keep in mind some people completely disagree with me but this is the way I like to grow