Humidifier?

You don't need a humidifier now but you might if you start another grow in winter when the humidity is lower. 60% is good for starting your seeds and veg. When in flower I like to keep the humidity closer to 50%.

They should be fine - you could put moisture domes over them (like a DIY propagator) but remember to leave akr holes for them, that will keep the humidity up. When they are bigger plants in bigger pots they will transpire more and the humidity will naturally get higher. An auto humidifier at least 5L capacity is a good investment. Bear in mind though, high humidity in flower can cause issues in a tent so keep air movement good.