LST can be started anytime, tho persoenaly id reccoment waiting till some of the plants have 3-4 nodes. Do this so that axuins(hormones) become centered at the top of the plant. Then when you do LST a plant the auxints will move quickly to branches that have already formed at nodes 1 and 2.
You can LST now, that would make your plants bushy also it would even out the quality and thc levels in all tops...Here again my opinions are such I like to have certain tops (main shoot) more potent then the others. This is so the potent ones are used by me or friends. Other tops are used in other things...
While reading your thread and understanding your issues looks like all is set to do good, those temps arent dramatic only uncomfortable. So the vent that you use in your window, you can make a intake there as well???
Also some of those duckting jobs you have could use a little work. The less bending in the duckting and the less the air has to travel the more efficient it is.
Those are just the things that i saw.
Other then that you are looking great !! GL and HF!!!