you said
"i can either place 12 plants in 11 litre pots in the space or 25 - 30 plants in 6 litre pots "

i have worked with similar space, and prefer less plants w/ more veg time. why? (1)law enforcement/plant# (2)less maintenence (3) more space for individual plants to enjoy. (4) yeild unaffected. ex. grow ten 1oz plants, or four 2.5oz plants with slightly longer veg. many methods you can use.
my opinion for 3x3 space = 2-3 plant, 3-5gal growbag/bucket

you said
"im thinking of FIMMING them with a curving cut of 75% of the highest node ( bud ) my question is if i had 1 kola bud that produced 1oz if i then FIM and 8 branches appear will it just divide the 1oz between the 8 kolas"

I do not have hands on experience with FIM. from what ive read its hit or miss when it comes to making the perfect cut through the node. i would GUESS you're on the right track thinking it would more or less divide an oz between more colas. but I DONT know for sure, hopefully with exp can help you.

I enjoy LST b/c no cutting is required. helps get light to lower branches. Good luck with everything