Hello! My chicks are 8 weeks old and becoming much too big for their brooder. The coop is finished but is it too early to transition them? I live in the northeast and we should be done with frost but some nights it still goes down to the 50s.
I've had chicks 5-1/2 weeks old go through nights in the mid 20's Fahrenheit with no supplemental heat. It sounds like you have not acclimated them to colder weather (exposing them to colder temperatures) but that is OK, many people do not. Yours have been able to handle a temperature in the 50's Fahrenheit for at least two weeks. Probably longer.
When they do eventually move in, do I need to re-dip their beaks in the new water source? Or is that only for baby chicks?
Typically no, you do not. But if you are changing the method of watering (going from bowls to nipples for example) you may need to teach them.
How do I help them learn to roost? They like the small one I built in the brooder, but will they just naturally jump up to the one I have in the coop? (2x4)
Roosting is an instinctive behavior. If they want to roost they will learn on their own. You do not have to teach them though many people on this forum do. With no adults around my chicks typically start to roost on their own at 10 to 12 weeks of age. I've had some start on their own as early as 5 weeks, some take a lot longer, but 10 to 12 is a good average for mine. Some of that may be because of what my coop and roosts look like. I certainly cannot predict what your specific flock in your specific coop will do.
My baby chicks in the brooder generally sleep on the brooder floor (I have a perch in there that they play on during the day but they generally choose to sleep in a group on the floor). Until they decide to roost my chicks in the coop sleep in a group on the floor. Until they decided to take their chicks to the roost my broody hens keep their chicks on the coop floor at night. Some chickens like Silkies that cannot fly (not all Silkies but some) prefer to sleep on the coop floor. Sleeping on the coop floor does not hurt them physically, mentally, morally, or emotionally. If you want to train them to roost as soon as possible, you certainly can. That will not hurt them either.
Lastly, do I put them in the run and they’ll just figure out how to get into the coop? Or do I put them in coop first?
You probably want them to sleep in the coop at night. Predator protection is better and they are out of the wind and rain. They do not instinctively know to go into the coop to sleep. There are two basic ways to try to train them to sleep in the coop. One is to lock them in the coop only for at least a week before you let them in the run. Often this trains them to go into the coop as it gets dark to sleep. Often, but not always.
The other basic way is to lock them in the coop at night instead of letting them sleep in the run. The way I do that is to go out as it is getting dark. They settle in a group (in my case under the elevated pop door) so they are fairly easy to catch. I lock them in the coop overnight. They eventually learn to put themselves to bed. I usually work in broods of 20 chicks. One time I did that and every one put themselves to be the next night. A few times I've had to be out there every night for 3 weeks before the last few went in in their own. What typically happens is that a few start going in after a couple of days and all are going in after a week but each brood can vary a lot.
Good luck!