My water temps w/ a chiller are constantly at 64-65 all the time. Yes, a chiller is a must imo to keep bad bacteria at bay in these types of systems. You are going to also need to run a sterilizing agent like h202 or zone, or run beneficial bacteria like hydroguard or some ewc tea. I run hydroguard in my system (switched from zone) and I could not be happier. If you are not running a sterilizer or beneficial's you will get root rot, almost guaranteed. As for vegging, your ladies look great, they will get pretty massive quickly so hard to say, but 4-5 weeks seems a bit excessive, depends on your room size and lighting i would imagine.
