good call on the humidifier. its always 55%-65% here so sometimes i forget.
for mine i stuck it in a 30 gal grow bag to start simply because seeds have taproots and the lower they go before getting constricted the better for growth. for clones i usually let them air prune and will gradually step them up. and yes, a 30gal grow bag is probably overkill but it never hurts to give them a little extra root space