I refer you to my original comment
My point is Isaan cities are not different from most of Thailand in any major aspect so to experience "authenticity" you just have to stray a mile or two from the shiny lights of the tourist areas.
A month of Songkran, . Methinks this has not been thought through, while it might be fun for a day or two I suspect it would become tiresome if it were every day of the average families 2 week break in Thailand. Do I not recall that the road death tolls rise dramatically during Songkran, is this a plot by the government to reduce the population?