Looking Good! Try filling up the pots leaving about 2.5-3cm/1inch of stem above ground to give as much space as possible for your roots to grow, also I'd suggest start training them once that new set of leaves pop out! (start with topping and slowly LST with main-lining to get good spread (or use ScroG method with topping).
Other than that plants look very healthy and happy!
Good luck and happy growing :)
If you wanna try for environmental perfection, then you want 50-60% RH at this point. I'm not sure that 40% would hurt your final product at all though.