Nice pictures! What type of soil are you using? you probably don't need nutrients yet if your in soil or just use really low strength. I started in seedling soil which is very neutral with little to no nutrients the little guys did fine for 4 weeks before I transplanted them. After transplant I put 3 plants in Miracle grow moisture control soil and they still haven't needed any nutrients and it's going on 6 or 7 weeks. I put 6 in Hempy hydro buckets and added 10-10-10 nutrients to them every watering. They needed more so I got some bat guano 10-2-1 and put that on top. Now I will just water for a bit.
When you go with soil you may be able to get away without ever adding nutrients, if you do need them too much or too little will be offset by the soils natural buffer and you should have pretty healthy plants with little effort. I am not sure about flowering because I have not gotten that big yet but I am sure nutrients are essential at that stage still not heavy though.
I would wait till you develop your first or second node before transplant. What you see now is merely the cotlydon, those will eventually die and fall off do not consider it your first node! Your first node will be the first fan leaves, those are the plants solar panels and are essential for growth. I think it's best to have those started before your transplant but it's really up to you.
Here's some food for thought so you can see just how long something can last in a little cup.
https://www.rollitup.org/cfl-growing/289369-3-strain-party-cup-grow.html