Would Love Some Help. 2 Plants 2 Squared Metres

This is my first grow so I really dont know too much of the details. I have built a box room in the garage and the floorspace is about 2 metres squared with a height of about 2 and a half metres. I have 1 400W HPS Grolux light and im growing 2 plants. I've got 12 litre buckets for plant pots and im using john innes no.3 soil. I am also going to use Biogrow and Biobloom later.
What i really want to know is how big can these plants get with all this space?
I also need to know about timescale, can i have them in veg for much longer due to the space?
I'm growing Chronic Haze from World of Seeds if that changes anything.

Thanks for any help you can offer.

You need to get a Ph and EC (ppm) meter too
Plans will grow until they outgrow their pot size and then they stop "growing", your 12l pot should be good for a 2 month veg and them bloom (8,9,10 weeks) and they will grow in size, how much no one can tell, but when you hit the bloom phase, your plant gonna grow for 50% + of her starting size
Happy growing

Thanks very much for the info. Do you think i could fill the space using the 12L buckets or would it be worthwhile getting larger ones and vegging an extra month?
I think what i want is basically two big mommas which i will flower and harvest

Bigger the pots, bigger the yield but you should think abouth plant size, couse when you hit the flowering stage they will strech! and them some!Mybe you should top them and then flower, so you save on some heigh.