hi there, lookin ok so far....but as said...you dont want to be using any addetives at this point, the plants pretty much grow by themselves at this stage.
as said root stimulators are only used for growing roots on a cutting which has no roots to start with.
if re-potting, look for a mild compost for seedlings and cuttings.

my preferance is liquid ferts, as they can be easily mixed in with water with no fuss.