Some answers[edit source]
Yes more effort is required, but in developing countries, allot of people would actually be happy to provide this work. Also wages are very low (0,5€ per hour I thought dpending on region off course), so some people shoveling a deep construction pit is actually not all that expensive. Also, perhaps in the future a open-source design for a small, low-cost mechanical shovel may be made
as for floods, indeed one should not build these structures in island nations. In areas away from the sea, I guess you may dig "wells" and stuff them with moist absorbing substances (eg clay) and moist releasing susbtances (eg sand) to reduce water buildup in the soil inmediatelly adjecent to the building
finally, yes earth sheltering always makes a buffer. Both in hot and cold countries, the building will be warmer. In cold countries however, the additional heating will make the heat and the earth will only function as insulation. In hot countries, it will perform more as a buffer and spread/dissapate heat from the radiation of the sun