Well I'll throw in my $.02.
I love my 400 mh, but I usually wait a bit to use it. I use floros to start off with, when they emerge, and keep them on floros till the first up potting, a week to 10 days. I plan on 3 upots to flower. If I'm in a hurry, after the uppotting, I get out the 400, about 18" or so away, as someone else stated using the back of your hand as a comfort buffer, if it burns you it will burn them.
Watering/feeding, I water/feed once form the top down, once just filling the saucers letting it wick up, at flower I do a whole pot dunk in a bucket of water/food.
I try to catch them before they wilt, but usually judging the need for water/food, by the weight of the pot. Hold it dry and remember it's weight...water/feed it, hold it agin and remember it's wet weight. As it gets lighter, see where they wilt a touch, and that gives you some parameters when to wet when to not. IMHO, less wet is better.
Feeding, some feed every time they water, I use PBP, @ 3/4 strength and feed at every watering. I also think plant strain will be different, but so far the 18 strains I've grown, show you real fast if they like to gorge, or prefer lite feedings, just watch her leaf.
If you leaf tips get a burnt look, your to hot, back off a touch. If she is paled out some and not over watered, touch up on the Nitrogen.
Sometimes in the path of a fan, will make leaves look leathery, so will over feeding, point your fans at a wall or straight up, and see if it helps the way the leaf looks.
Last point for a new grower, dont love them to death... it's a weed, she'll grow almost any damn place and under many conditions, but what I see most is new folk watering every 15 minutes, spraying, adding this suppliments or that one. It's all personal preference but for my gardens, simplisity rules.
Good luck, and feel free to ask anything, if I know I will say so, if I dont ...I dont!