i used 12/12 to find my sex but while doin so i had some in veg still that sexed before the 12/12 sexed...it all depends some strains are autoflower and will flower in veg still...i dont recommend the 12/12 then back to veg...if you start 12/12 jus do 12/12 the rest of the way...as far as the 2700k you should add for flower but a wider spectrum is better like 4 2700k 2 6500k somethin like that