all depends on the strain.....you could get a plant that finishes in 2 mnths or 1 that finishes in 16 weeks....and u prolly wnt yeild alot unless ur a good grower....expect a quarter,maybe a half unce....but sme ppl have grwn buds that weigh over an ounce frm seed...good luck!
Dont get a box get a cabinet so you will have more height. You wont get much from seeds going straight into 12/12 but if you have clones from a decent sized mother, you can put the into flower right after they make their roots in the clone box and get fast bud decent sixed too but nothing amazing although in the end you get more bud than growing a couple big plants since you are getting a steady supply fast : ) Good luck.