If your growing in soil you don’t need to add nutrient for the first month at least, if you do it may lead to nutrient overload and burn.
This is where a slurry sample will come in later when you have the PH and tds pen.
18hr a day for photos or 20hr a day for autos while in veg.
Learning about how to dial your lights in is important, read this thread and toss me a like on it, lighting is one of the most important factors for end bud quality.
Sorry you have a 2x4? Or 3x5 tent?
It depends on how well you grow them either way 4 is good for right now,