a just rooted clone only a few inches tall thrown into flowering could very well get 10-20 inches tall while its flowering so your estimates on height is probably close for most strains.
and if your are running 4 plants per sq ft you may have to do some pruning of some of the side branches so the plant will only focus on growing a single cola and also to allow more light to the other plants.
flouros do have a purpose for veg state or rooting clones or even keeping a small mother plant but when it comes to flowering you should only use a hid there really is no subsitute for a hid light for the lumens they put out while they do produce heat, and ventilation to cool them only adds to the cost there isnt really any other option and still have a good yield.
when using pots they should be deeper when used for a sog as it does increase the amount of soil available for the plant to develop roots, another option would be to use a soil bed and not use pots at all.