If you put your chicks in the coop at 6 weeks old, you might need to add some heat at night (depending on temps).  Our 4wk old chicks went outdoors last May and it was still cool at night, so we kept a heat lamp on them until they were about 10 weeks old (early June).  They did fine.  But I didn't provide any supplemental heat this winter - didn't need it with full grown chickens, their feathers do that for them!  The puffed up like basketballs on really cold nights, snuggled up against one another and were fine.  
 
When we started letting them out into their run when they first arrived (took me a couple weeks to finish the ramp, door and run area so it was predator safe), the first few nights I brought out a treat about 30min before dark set in....some warm oatmeal with raisins, some finely chopped up scrambled eggs, some leftover corn muffins, etc.....so they learned that REALLY good things happened inside the coop about dark.  By the fourth night, they were inside waiting for me to bring their bedtime snack!  I kept this up until they were nearly fully grown (18wks or so) - just because I wanted them to grow!  Now, they get a 'dinnertime' snack....I feed our indoor pets dinner and bring out a snack for the chickens long before dark, but they put themselves to bed just fine.  They instinctively know where safety is - and seek it at dark, as they are nearly blind in the dark. 
 
Good luck!  Enjoy 'em while they're little!  It goes super fast!