i would not change the light cycle leave it at 18/6 at all times in vegging stage with you pulling the cycle to 14/10 that could stress the plant out and turn it male and i would stick to the same light too cause a change in light couls also stres out the plant
the cyclces are 18/6 or 24/7 for vegging personly i do 18/6
so the plants have a lil cooling period
and the flowering cycle is 12/12
yeah it is possible to bring a flowering plant back to veg stage as long as it isent too long into the flowering cycle
you need to flower the plant to determine sex anyway but this usaully shows in the first week or 2
yeah you can crowd them into the chamber when they are that small
as they grow you will probally have to change them around or get a bigger chamber
if ya can post pictures of ya setup you will get a better more acurate responce to ya questions
cheers hope this helps