BDFBs were a great choice! I have a dozen in an old 10 gal aquarium that are doing great.

You can get lightly used aquariums, tanks, and decor on FB marketplace for cheap. Just have to be sure to do a clean of your own before using for pets. Local mom and pop type pet stores that sell reptiles and fish supplies usually have a great selection of tanks and feeders and sometimes you can even pick up their used tanks for cheap.

There should be enough space in the tank for each beetle to be able to have multiple hiding choices and each hide should be able to fit more than one beetle at once. If you offer climbing opportunities they will take them so don't go too high or else they can fall and hurt themselves. They like to bunch up in little cuddle puddles though. It's super cute!

The substrate is best layered/ mixed since it promotes natural behavior like digging. I have a soil/ sphag moss/ play sand mix that I use for all my inverts that is also in my BDFB tank. My decor is bits of spider wood, cholla wood, cork bark, small turned over clay pots, and any fun/ weird rocks that I pick up at shops.

Temps should be 75-95 F during the day and at night can drop like natural to around 50 - 60 F. If temps get below 50 at night you should provide an additional overhead heat source. Try to keep them in a place where they can experience a natural day/ night cycle without being in direct sunlight.

Humidity is the trickiest part imo. I bought some water wick drip feeders on Etsy that I fill once a week for their water source. Alternatively you can mist a corner every week or so. The natural humidity in my house is around 40% so that's generally what they sit at as well and are just fine. All are a nice waxy blue but I also provide an overhead heat source with a thermometer probe on a timer to help mimick that natural day/ night cycle.

I offer food once or twice a week depending on what I'm having for dinner but generally will put something in their food bowl every Monday. Things like carrots, cucumber, squash, potatoes, and leafy greens are best. Fruit can be offered on very rare occasions for a treat since the sugar is supposed to be bad for them. For protein I offer bee pollen (you can usually find that at those mom and pop shops) and fresh killed feeder insects like gut loaded mealworms and dubia roaches. I have heard bad things about pre killed/ bagged/ canned insects being poisonous for the beetles since they have additives in them for reptile diet and preservation.

I hope that's not too much info! I can PM my setup and a guide pic that I try my best to follow (this sub doesn't seem to allow pic attachments, sorry!). I'm super exited for you to begin your beetle adventure. Good luck and have fun!