Regarding using a used home-heating oil tank for water storage:
If this is for general water stoarge, you may be able to get the interior of the tank clean enough to be used for washing / bathing, but I would not expect to be able to use a tank which once held petrolum for potable water. It would be nearly impossible to clean the interior of the tank sufficiently to prevent contamination of the water with oil products, sulfur and other poisonous substances.
In addition, the interior of many of these older tanks would not be lined to prevent 1) rusting or 2) contanination by metalic leeching when exposed to a humid enviornment - The manufacturer expected a fairly constant layer of oil to be on the interior side of the tank.
For buried storage in New England, I believe the recommended depth is 4' (This is called the frost line) You should be able to call your town building inspector and ask him what the "Frost Line Depth" is. The top and all pipes for the water should be below this level to prevent freezing.
Multiple spread out tanks with seperate feed lines and ball values makes a lot of sense. I have considered adding a couple of 82 gallon pressure tanks to my house (I currently have a 40 gallon pressure tank) These store water while maintaining house water pressure, so they are constantly filled and cycled by the natural use of water in the house. A series of ball valves allows you to manually add or remove tanks while spigot values would allow the draining of water without passing through the house pipes. Add to that a couple of rain barrels for collecting fresh water for irrigation and bathing, plus some off-line storage barrels for holding water should the well become unuseable and you have a nice solution for water storage.