Welcome aboard Jax, as always, good to have you along, cheers.
OK,..with the leaf wash , use it right now , before the buds form and have started to push out pistils...u will be fine. As far as the exhaust fan,...i highly recommend you get a good quality 6 inch fan and a Can #33 filter. That 5X5 will need a good 6 inch , that you can tone down a lil , like 70-85 % and not have to have it running and screaming away at 100% all the time. If you over size things a lil , it makes everything else much , much easier to control.
With your NYC D, keep an eye on her leaves...they will tell u how how heavy/light to feed . Pay attention to leaf attitude and color OK. Cheers bud!