12/12 from seed is probably fine. 1 sq ft per plant. Keep vege short or as short as possible and should be okay.
as far as whether or not the buds will 'tighten up' is a matter of genetics.
Yes, you'll maybe to make use of the light upgrad. Efficacy varies so watts are not the right metric to use. .64m^2 x 860 --- Any light with 550 umol/s PAR production will be a good size for that tent.