Your plant is going to love having that HPS! You should see some noticeable difference in bud production, and in much less time. Looking good, I hope you enjoy the harvest.

As for the yellow leaves; it's pretty common to see this during flowering, when the plant should be receiving much less Nitrogen, and more Phosphorus and Potassium. I will take off the leaves that have shriveled and died after turning yellow, but you should leave as many on the plant as is possible. You can trim some if they're getting in the way, just don't go overboard. Your plants will rely on most of the fan leaves to help produce healthy flower clusters.