How about four 48" wide tanks, such as 75 gallons?
Or a couple of 72" wide tanks, such as 125-150 gallons?

Your real limit on a long tank will be the length of glass your local glass supply shop can order in. That will be some standard length at a reasonable price, or a custom length at some not very reasonable price.
Sounds like fun for someone who can afford it. I look forward to seeing pictures in a couple of years.