Day 7 too early to feed wait until about week 3 and give 1/4 rec. dosage. I do not know about the food so I will not comment, nut it seems more for flowering.
Yes it's usable, but first use some patience. Read the grow faq on this site. Then ask a more informed question that details what you are growing in and has pictures. If you insist on using your Schultz product, use it during the flowering stage.
yes, those are very useful. i use botanicare's pure blend pro lineup but the triflex is good also. read on the back of the packages what ammounts u should use for soil. i use mine in hydro but i dunno how much that should really matter cause all my shit is made for soil also. yeah dont feed now they are way to young and u could kill them. wait until at least 2-3 weeks into it. just follow the destructions on the bottles.