Setting Up My New Grow Tent (NEED HELP)

Experience. Personally I think you are going to have a hard time controlling the heat in that small of a tent with a 600 watt. You may get away with it b/c you have an inline fan but I think it will be tough.

If you dim your light down you won't get the full benifit of the bulbs spectrum. You should have bought a 400 watt light IMO.

To answer your question about what else you need is exhausting but here's a small list:

Ducting, hanging chains, buckets, soil, seeds, fertilizer, small fans to blow over the canopy, a medium size oscillating fan on a timer, a timer for the light, an intake fan, shade 5 googles so you don't ruin your eyes, a book on how to grow marijuana, duct tape, ring worms, a temperature and hygrometer meter with beacon, drip pans, mason jars, a hygrometer for curing, extra bulbs so in case one bursts you'll have a back up immediately, etc.... Good luck. We all started somewhere.
I'll share my first rookie mistake. Don't ever spray buds in flower, ever, you'll get mold/bud rot.