My rule of thumb is that the plant should be about 12" high before you flower it. By the time it's done, it is typically about 36" high. Since you're outdoors, you can grow those suckers as high as you want. The brown leaf tips are definitely nute burning, so just give those plants just distilled water for a while until they start to look needy for nutes. Be careful about topping those plants. Research if the particular variety you're growing should be topped or not. I had a friend that topped four plants that are supposed to be topped, and he got as much off them as the 16 plants he didn't top. Some like it, some don't.