Afraid of over watering / over feeding

My plants have had a rough start but I haven't killed them yet! I transplanted from solo cups to 5gal smartpots with coco/perlite a week ago and they seem to be doing ok although not great. New growth is green and normal with what looks like the first signs of sulfur deficiency which is understandable as I haven't been feeding them at all because I over fed them in their cups. I've ben trying to water them sparingly around the edges of the 5gal pots so the roots will grow out. Yesterday I gave them weak light nutes 330ppm @ 2 qts each around the pot edges which doesn't give any run off. I guess my question is, how can I tell when it's OK to start really watering / feeding with runoff without messing up root expansion in the new bigger pots?

Water/feed them when they are dry and need it. Usually 3-4 days between for plants that fit their pots. From Solos to 5 gal is too big of a jump (unless they are autos). It can take those up to two weeks to dry out with so much dirt and so little roots. Solos to 1gal, then to 3/5 gal pots depending on what you use.