I have made the round trip from ATl to BHM many times.
Sometimes I have come and gone the same day, sometimes I have spent the night, as you will note below. For your trip, if you feel it is long enough already, it is probably not worth it to spend the night but my thoughts below anyway.
Always concerned about o.t.(if I am comng and going the same day) I usually wait until the "morning of" to make my reservations, just to be sure the s.b is on time. I call about 6, and if it is on time, I make my same day reservations then,and pick up the ticket at the station. That usually will not jeopardize your chances of getting a seat because the train usually has its biggest load between WAS and ATL, not NYC and NOL. That is my advice. Unless you choose to stay overnight in BHM.
What I have seen of downtown BHM is rather dead. there is a library, a civil rights musuem, and an IMAX Theater, a couple of nice htoels, not much large retail. But it is adequate to walking around about an hour and a half. I am not sure if I remember a restaurant called "John's". You might try the internet to see if it is on there.
There is a large shopping mall way out in the suburbs called Galleria Chase or something like that and there is a neat hotel physically attached to it called the Wynfrey, I have stayed there several times. I was stuck there durng the genuine blizzard ("Winter Storm" all across the southeast and northeast) of 1993 for a couple of unscheduled days. Another story, another time.
There are no lockers to store your bags at the station in BHM for a one day round trip, so you check with the one person who is doing everything at the station, selling tickets,loading baggage, etc. and leave it with him. Kind of a hassle pinning him down. Best to travel (round trip one day) with zero luggage if you can. That man might be very nice but he is very busy. But just charges about a dollar, last time I did that.
There is one of those nice oldie-goldie but well maintained older hotels in BHM. It is called the Tutwiler(spelling?). Very expensive but sometimes you can find good rates, even half price. Done that a time or two. Nice, though not large, eating space. I would not rank it with something like the Royal York in Toronto, but it is along those lines. Most cities seem to have at least one such well maintained older downtown hotel.
The station is on the very outskirts of the specific downtown area proper, so walking around to most places is easy enough.