Yes, a 24 bay IMO is better than the 36's because you can fit a full sized GPU in them. If you get a 36 bay, 12 of the drive bays are in the back of the chassis and that puts the motherboard tray above those 12 drives therefor making the motherboard "compartment" only a 2U section. So you won't be fitting a full sized GPU in there, and you will only have a handful of options that would be worth even having in there....
I am telling you from experience, I bought a SuperMicro 36 bay 4U chassis and wish I would have only gotten a 24, simply because I would like to be able to fit a full sized GPU in it.
Other than that, I would highly recommend one of the SuperMicro's... I got mine from The Server Store for around $600 shipped. It has 36 hot swap bays. You can buy a barebones chassis, just the chassis with PSU's... Check em out, if you have any other questions, feel free to shoot me a private message.