Without knowing the actual loads it's impossible to make reasonable suggestions. Start by hiring an engineer or RESNET rater or similar third party company (and NOT an HVAC company) to run an
aggressive (not conservative) Manual-J load calculation, at the 99th percentile temperature bin for your location, and at 68F indoor, not some colder temperature bin or warmer indoor temperature. If you leave it up to a typical HVAC contractor you'll end up with something 3x oversized, resulting in lower comfort, lower efficiency, and at a higher up front cost.
If the snow melt is at the same address, run the snow melt as an isolated zone off the space heating boiler. Snow melting is a fairly low an short term boiler load, and for 1000 square feet would not affect the sizing of the boiler.
If you are heating the domestic hot water with the same boiler, that only affects sizing in rare instances, such as 150 gallon luxury bathtubs or dual head showers with a half dozen sidesprays, etc.
Then it's a matter of finding a reliable boiler manufacturer that has good support in your neighborhood. There are many good brands, but even the best brand can be brought to it's knees by incompetent installation combined with inadequate local distributor/manufacturer support.
The load numbers should be calculated room by room, and sub-totaled by zone, since the size of the zone loads also affects which boilers are good, and which are better.
When you have narrowed it down to a few models & manufacturers it's useful to call the distributor to get a few names of competent installers working in your area, since they are in a position to know which contractors are installing their boilers by the dozen without complaint, and which ones are turning in warranty claims for failures related to incompetent system implementation, or keeping the tech help line tied up with questions already spelled out in the manual.
New York is a big state- got a ZIP? That might help in determining the amount of local support would be available for different manufacturers.
Also, if you have a heating history on the place it's possible to determine the whole-house heat load (but not the room by room or zone by zone loads) based on comparing the fuel used by the existing boiler against heating degree-day data (use only wintertime data, if you can), as outlined in
this bit o' bloggery. If you are looking or a modulating condensing boiler, not merely direct-vent, you may want to
review this as well.
