Gonna be hard to pull worth while cuts off of those seedlings at this point without shocking them, best to top or fim and once that grows out take a cut. It looks like the issue at first was being root bound. It is a hard thing to tell when in Dixie cups, now you have some nice pots. I always look at the drain holes on my 1 gallon pots to see when roots are pushing out. Once 1/4 to 1/2 the holes are showing roots it's necessary to transplant to keep the plant healthy. If you're transplanting into fresh, good grade soil there are plenty of nutes right out of the bag to go for many weeks without needing to add anything. Watch for the overall plant (not new growth necessarily) to go more lime green before adding SMALL doses of N or even N with a Cal/Mag nutrient to the soil or water. Try and rely on that Age Old mix or a compost/EWC tea for foliar feeding under and on top of the leaves once a week if the older growth doesn't seem as dark which also helps with pest prevention. Once nutes are in the rhizosphere, if tips start to burn you are looking at more 'flush work' to get back into balance. IMHO light, water ph (and declorinization), and pest prevention far outweigh nutrient addition in most new gardens. Nutrients are largely marketed to the 'newer grower' giving a false sense that they alone will give you boom harvests. Whatever you do, get a notebook if you already don't have one and document (and take pictures) so you know year to year what works, that was the single best piece of advice an old-school cultivator gave me. Capulator said it best "Keep them happy and be PATIENT".
