If you are using Hydroguard or similar product you should add that. I would wait until they get their first set of true leafs and then give them 1/4 strength nutes. Doing a res change is up to you but if all is well then you can wait until the week after adding nutes. I found that keeping the res level higher (2"-3" from the bottom of the pot) helps with root growth, oxygenation of the solution, and reduces root problems and maintaining reservoir temps.