I do believe I read that clones can be taken, rooted, then forceflowered to figure out what your others are going to be. Is this fairly correct?
That is correct.

Grow cab better to be taller and narrower, or shorter and wider? Taller and narrower is what I'm thinking.
Well, probably taller, but that depends. As long as your temps at the top of the plant are ok with your lamp at, I suppose, around 1 foot, and the plant has room to grow about 2 -3 foot with the lamp moving up at the same speed, thats the height you need.

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