Welcome to BYC. Glad you decided to join our flock. X3 on sourland; you won't be able to keep them in that 40 gallon aquarium for long. If you haven't done so already, definitely check out our Learning Center at https://www.backyardchickens.com/atype/1/Learning_Center. There is lots of useful information there. Please feel free to ask any questions you may have. We are here to help in any way we can. Cheers.
They will also fly to the top of the brooder a lot sooner than you think. They can hop or fall and not be to get back inside. Please have a wire top to contain them and keep pets, etc. from getting to them.
Welcome to the BYC flock! We are glad you joined us!
That might work for about a week, tops. I would start looking for an alternative soon. You may try calling around to some appliance stores to see if anyone has a large appliance box you could get for free.