Well, depending on the area that you live in, I don't think your seedlings will make it to the end of March before they flower. Unless of course, you have them under lights at an 18/6 hr photoperiod. If they are taking in natural sunlight right now, chances are they will start to flower before the end of March. This is not good, because they will be small and it is really not good for them to go from flowering back to veg when the days get longer. As for nutes, I've found much success with the Botanicare line of nutrients: Pro Grow(for veg), Pro Bloom(for flowering), CalMag, Liquid Karma, and Sweet. Make sure you go to the website and get the feeding chart which will be very helpful. I also add in some unsulfured molases right before I flush and at the very end of flowering to get a rather sweet taste. Be aware with molases though, ants love the stuff, and if you use it too soon, they will infiltrate your beautiful flowers.

Hope this helps,
rider