[420'ing]

Hi all,im new to here and growing in general so im looking for some advice,especialy as to when i should start flowering!
I have a growtent thats 1m X 1m and 2m in height with a 4inch Ruck extraction fan and a carbon air filter.Im using a desk/office fan for air circulation/stem strengthening and have a 400 watt HPS light about 10 inches away from the plants.
Im growing 4 Cheese plants(lol) bought from the greenhouse seed bank and they are growing all very nicely as far as i can see,all about 4-6 inches in height with big green leaves and starting to branch off already......they are all 13 days old now,i have pictures of them up untill day 11,i'll take some more in the morning!.......
What i need to know is when should i be starting to flower these/change pot?Is there any height i should wait for them to get to before i start the flowering cycle?
I was planning on veg'ing them for 4 weeks before switching over to the 12/12 light cycle,is this too long or too short a time?I
want as high a yeild as possable in the space i have!!!!Should i be doing more plants, or less plants???Im looking for personal opinions aswell as good advice!!

Thanks for your time!
420'ing