Im not too sure how much you will get, a lot of that is up to the grower and his/her setup (Pot size, nutrients, lights, general care, etc...). With a Hindu Kush plant your probably going to be yielding between 1-3 oz (an oz is about 30 grams). Now as for changing to the flowering stage... it is really up to you. Once you are happy with the size of your plant you can start to flower. The larger the plant is when flowering starts the larger the yield will be typically. The veg stage will go for a number of weeks, and you will typically want to start flowering once it hits at least 20", no shorter than that.
Now for nutrients, I am not too familiar with clones and nutrients, but I am assuming you will want to wait till an actual root system develops before you start using nutrients, so wait maybe a week or two before adding nutrients to your water. As for when you water with nutrients, you should probably give your plant nutritioned water once a week, maybe twice if your water isn't too concentrated. If you see some yellow discoloration in your leaves, this MAY be a sign of over fertilization in which case you wanna water without nutrients until your plant starts to look a little better. If that doesn't help just check around the forums for other possible reasons.
