At ANY per kwh rate with the seasonal heating required anywhere in NY state heat pump technology would pay for itself. If you're already committed to the electric boiler concept, size the boiler to minimum of what you need now, and when you graft on the new dream house do the financial analysis on what a variable-speed air source heat pump (ductless or ducted), or a ground source (geothermal) system would deliver. But doing that financial analysis NOW may make even more sense.
You may be able to cut your heating costs by maybe a third to half by going to electricity, but why stop there? Propane is currently the most expensive heating fuel possible where electric rates are cheap (at about the national average or higher pricing on electricity your electric boiler might be more expensive), and heating with a heat pump in cheap-electricity-land will be something like 1/4 the cost of heating with propane, maybe even less. Even with the prospect of a future lower price on propane locally as the Marcellus & Utica shale gas fields are developed, it's doubtful that it'll ever approach heat-pump technology on a BTU/$ basis, even if the price of electricity doubles.
And with heat pumps you also get air-conditioning to take the sticky edge off the hazy heat of July.
With any heating system it's important to get a good handle on the size needed, and you may not need anything like 62000BTU to keep a 1500-2000 square foot bungalow warm (even at -25F outdoor temps you might see in Saranac or other higher-cooler place.) If you've gone through at least a heating season or two on propane and know your annual fuel use it's possible to get a fairly good handle sizing based on fuel use, heating degree-day data for your zip code, and the nameplate efficiency on the propane boiler. (My at -25F the heat load on my ~2200' bungalow w/1500' of semi-conditioned insulated basement is still well under 50,000BTU/hr.) If you don't have that information, "manual-J" type heat loss calculation would get you there.
Even a single 1.5-2 ton ductless mini-split heat pump would likely handle the shoulder season heating loads, at an operational cost a third that of an electric boiler, and it's contribution to the mid-winter heating would be at ~half-cost relative to the electric boiler. Geo would even be a bit better, but would usually be a much higher up-front cost unless subsidiesed. (A 2-ton mini split is ~$5KUSD, installed, in my neighborhood, but 2-ton geo runs ~$15-20K, often more.)