I'd agree with with Puffer punk for long tanks, but I've learned one thing as an exception.
My 8 DP are happy in a 24x24x30 tall, but there is driftwood stacked from top to bottom.
The roost in the nook of the branches at night and cruise all levels of the tank cleaning house of any pest snails.
***Use lots of driftwood and plants.
They are very fat and love to stop what they are doing and cruise the front glass as soon as a human comes in the room.
It is basically the same as what you see in a pet store, but we feed our puffers.
They will stare at you through the glass like dogs.
I'd still suggest the long tank as it it easy to clean.
They do make a nice 48x15x16 from Seapora with a long glass lid and a center glass brace for about $110.
40 breeders with the support of a center brace are better than those weak non-supported 40 breeder we all find on sale.
The glass bows way too much without center braces on most tanks.
We have been adding Anubias nana petite (plants) to the tank over the past few weeks.
The nana petite are pricey running $4-5 each little bit, but grow well in the right light and better with fish waste.
They are a good low/medium light plant.