A friend of mine recently purchased a baby betta from Petco without knowing the care they need. Once they got home and got on the net, they decided they could not give the baby the care it needs. Here's where I come in

I'm known as the crazy fish/cat/bird lady amongst friends so they called me up and asked me if I could take it. My betta recently passed and I have a pretty decent setup so I said I would take the baby.
I have two different setups and I'm curious as to which would be a better environment for a baby. I have a five gallon eclipse hex with a modified filter (reduced current) and a heater that keeps it at a constant 78 degrees. The other setup I have is a one gallon tank with a small heater that keeps it 82 degrees and a Marina i25 filter. There is no light on that setup, but it has a lid.
Should I keep the baby in the one gallon until it gets bigger and then transfer it to the five gallon? Or should I just start with it in the five gallon? I have not seen the baby yet, so I do not know what condition it is in. Also, I was going to get Hikari First Bites... any other food I should pick up?