Seedlings in their first or second week do not need many nutrients but they have to have some, particularly in DWC.. a ppm of 200-300 is ideal. You can increase the ppm by 100-200 every week... Keep the roots/water without light so bacteria doesn't grow... and start a diary for this grow! My first attempt at DWC was hilariously filled with mistakes and the plant has suffered a lot - but is still growing well and going to be great... my second DWC has benefitted from all the learning those mistakes made me do... If you can get it down, if you can learn, you're going to love DWC....
Good luck!