1.) Well if you want some decent weed to smoke, then you have to kill the plant...it can be re-vegged but it is difficult...it is less difficult to grow a new plant(i think), or take clones...

2.) lumens...well i don't really know, so i say nothing...
for myself...i have 4 small plants under 8000 lumen....

3.)One plant for one person? depends on how big the yield is, and how much you smoke..