My tent is a little bigger than yours, I grow one plant at a time. I often start one plant while another is finishing, but that's about it.
This being your first grow, I'd also start with one seed because it's easy to screw up. We've all done it; and seeds are expensive.
Read up about SOG and SCROG and other training techniques. You might want to try them later.
600 watts in that size of a tent is a lot. You would have heat problems. I have a 400 watt HPS, and I can't grow in the summer because temps keep going into the 90s in the tent. You wattage is about where it ought to be now. If you want a 'kick' consider led, but be careful you don't get a lamp that is too strong.