Required PPMs are going to vary from strain to strain. Also, the overall health and age of your plants play an important role in their ability to take higher concentrations.
We would need more information before anyone could make an educated guess to what would be considered acceptable for...
If you cut a side branch along with the main stem, I would go ahead and top lower. You've got nothing to lose but height, which will in turn create a sturdier base for your buds to hang on.
No worries...:bigjoint:
I've seen a few people use Miracle Grow with mixed results.
Do a search through the forums for "Miracle Grow" and see if you can find some. It may give you an idea... :bigjoint:
Yes, it will affect it. Will it be detrimental? Not Likely.
A week of reduced light is only going to hurt growth and maybe cause a little stretching. Keep the lights close and you should be OK.