When you let a strain go to seed the offspring will probably be different than the parents. So I'd say get a variety of seeds and let them breed as they want. If you switch to 12/12 light soon, like after a few days, the plants will have very little vegetative growth and so should be short short. I've been thinking that it would be a good idea to get one container that you can plant all your seeds in, and let them grow in there and go to seed, and just keep perpetuating as the seeds fall off, and you can thin out unwanted plants if they become too crowded.