My .02 says that it is easier to maintain fire through the summer and keep the basement dry and the boiler is excellent shape. The cost cannot be that much different than the electric water heater, and your investment in the boiler and piping will certainly pay back over a short time. If oil remains in the $3.00 range, you will be in a two or 3 year payback......what other heating equipment will do that for you and your family?
You will probably shut down for a few days during a non critical time to clean and service the boiler, anyway.
Be aware that you can include your electric water heater in the domestic coil loop if you chose, so that it doesn't sit idle all the time. A bronze circ is required for all potable water connections.....think about that possibility.
My take on the daily usage would be in the 25 to 35 lbs a day average....some heat on a few cold days, and standard hot water usage. You won't have any out-fires in my experience, and ash container changes every 4th day give or take.
Many folks shut down in late March or early April, and there are still lots of cold days, so having the boiler online eliminates a more expensive fuel to chase the chills away, simply keep it loaded and empty the ash container.....