Yes look into lst which is also known as low stress training. And as long as it is not an auto flowering strain then yes you can take clones but make sure you have a separate area for them. Going 12/12 from seed isn't exactly what it sounds like as the plant will veg roughly 2 to 3 weeks anyways regardless of light schedule
You could top it now as well, clone the tops, then throw them in there as well
and Fimming doesn't cause stress similar to topping?
If you are starting from seed and going directly into 12/12 I wouldn't do any sort of topping or fimming because it will just slow down the flowering process.
It doesn't slow it down that much In my experience maybe 3 to 7 days tops.
Well in that case let them grow the natural way lol