@sunnie7 one of the best things about BYC is helping the beginners!
The light overnight is one of the reasons that I switched to the plate brooder. The chicks actually seem to like the light, but in my opinion, they need the dark sleep time too. So its a toss-up. But once they are fully feathered, you really won't need it. Chickens are much tougher than we sometimes think. They will generate plenty of body warmth in the top of that coop.
I have not used the cookie tins (my husband didn't like the idea) Closing the door is up to you. If they don't want to stay inside at night, you can close them in and they usually learn its where they are supposed to go. And if you have any worries about any predators, it is probably best to close it... plus, closing it will hold the heat in better. But otherwise, it can be left open.
I put food and water underneath the boxed-in part. I don't think there is a "right" place to put it. It kinda depends on how messy they are with it, where is convenient for you to re-fill, and clean, etc. You want them all to be able to gather around it, so they don't fight over one spot. So you may try different places to see what works best. I wouldn't put the food inside the top part though. Especially if they will always live there, the top will be where they will sleep and lay their eggs. Keep the food somewhere down on the ground. I do put food in the top when they are tiny and before they can go up and down the ladder, but that doesn't last long at all.
Have to show this pic. This was before I moved that coop outside (yes, it was sitting in my dining room for 4 weeks!! lol)
I had ducklings in the bottom, and chicks in the top... lol
