As long as it is in vegging mode, you can take a cutting or small branch and put it under 12/12. It will start to flower, revealing it's sex. I think it's necessary to root them a little 1st, but it could be done at the same time as the switch to 12/12. Cuttings or clones are usually harder to root once flowering, especially Sativas.
Cloning is easiest during veg growth...in my experience, they can be a bitch to root or clone when flowering. My buddy who does the cloning usually clones them using something offbeat, like 14/10 or 16/8 sun/dark. The result is usually a clone that is somewhat confused as it is sorta stuck between growing and flowering, throwing a bunch of 3 lobed leaves and pistils. When I plant them under 18/6, they explode in new growth as they swing into full veg mode...but they are very different than the parent plant because of the bushiness. FWIW, you can re-veg full plants if you try hard enough, you just have to leave a little more leaf and branches on the parent plant than normal, and maybe don't let it finish to the point of plant exhaustion. Its a great idea if you are thinking about moving a grow outdoors..the time of year is right for veg growth and the photoperiod works out great...and you don't have to grow an entire new plant. It will grow like a mutant and flower like normal...but your yield will be great!!
Where do you live?
There are a LOT of Urban Legends around when it comes to growing, with some having a kernel of truth while others are pure bullshit. When I either sprout a plant or grow a cutting, I leave it alone for about a week. The roots will grow like crazy on their own and don't really grow any better roots by cutting all of the leaves off. I don't use LED lighting for the most part...is that 2000w at the wall or 2000w equivalent? If using an HID, I would probably go with a 600w bulb...it's hard to compare them because there is no fixed conversion for them...1 mans 2000 watt system is another guys 4000 (or 1000) since they are hard to compare apples to apples. With your limited space, you will want to focus on training the plants to stay low and stretch the branches out horizontally as much as possible. I've never tried SOG or SCROG growing methods, but people have had a lot of success with this process.
People cut the leaves so that total transpiration is reduced, so the cutting doesn't wilt and die before it roots. Its not necessary if you have moderate temps and light, and a humidity cover, like you show. Lots of guys just just a regular sandwich bag.