First, measuring the baseboard has nothing to do with sizing the boiler, and the boiler should be sized for the heat load of the house. With zip code we can calculate the heat load at the 99% outside design temperature for your location based on your fuel use against degree day data and the boiler & woodstoves' approximate efficiencies (see example below).
Anybody who uses rules like "lessee, 130 feet of baseboard times 600 BTU a foot comes ta 78,000BTU/hr", or " OK, 2400 square feet times 30 BTU/foot is 72,000 BTU" then rounds up to the next boiler size "just to be sure" is a hack. The boiler they install is reliably oversized often by 2x or more- it'll never leave you cold, but it'll take a hit in efficiency, maintenance and often comfort to boot. Those methods are common, but should be banned from the industry, IMHO.
Every good system design starts with a real heat load calculation. If not ACCA Manual-J, at least use I=B=R methods, or when there's a good fuel use history, calculate from there.
Most oil boilers in 2400' houses in CT are at least 2x oversized for the actual design-condition heat load, so don't be surprised if we come up with a much smaller number. But being more than 1.6x oversized on a cast iron boiler means it probably won't hit it's AFUE efficiency, and at 3x oversizing it's slipping down the steep part of the efficiency regression curve. The length of the baseboard might give a sense of whether or not you go with a condensing boiler though. If you have enough baseboard so that it can deliver enough heat at the 99% design condition with only 140F water you should be able to hit the mid-90s for average efficiency.
Using an embedded coil for domestic hot water requires significant oversizing of the boiler to deliver acceptable hot water performance, and has abominable summertime efficiency (for almost all cases.) It's worth installing an indirect operated as a separate heating zone and sizing the boiler correctly for the heat load.
It's possible to get 86-88% 2 & 3 plate cast iron boilers that are sealed combustion/direct vent, and that's probably the right thing to do if you're not going for a condensing unit. Anything over 83% can't be vented into a terra cotta lined chimney without running into flue condensation issues, and the chimney is probably oversized for a boiler that is right-sized for your heat load. The additional cost for the boiler upgrade will probably be lower than the cost of installing a flue liner, but either way, by going sealed combustion/direct-vent you have zero chance of backdrafting, and don't have yet another flue driving outdoor air infiltration 24/365. (All condensing boilers are sealed combustion direct-vent.)
For yuks, using the fuel use method of measuring the heat load, let's assume you're near Hartford (design temp = +6F ) which averages about 6000 heating degree-days (base 65F). Let's assume your boiler has a steady state efficiency of 85%, and your wood stove is 70%.
At 138,000BTU/gallon your 85% efficient boiler delivers (0.85 x 138,000=) 117,300 BTU to the heating system sends the rest up the flue.
For 850 gallons that delivers 99,705,000 BTU to the system over the course of a year.
Assuming you're burning something local like red-maple you have a source fuel heat content of 18,700,000 BTU per chord, but in a 70% burner that's delivering (18,700,000 x 0.70=) 13,090,000 BTU per chord to the house.
For 1.5 chords, that's (1.5 x 13,090,000=)19,635,000 BTU of heat delivered to the house in a season.
Combined, that's (99,705,000 + 19,635,000= ) 119,340,000 BTU for a ~6000HDD year.
So per HDD that's (119,340,000 / 6000 )=19,890 BTU/HDD
With 24 hours in a day, that's (19,890 / 24=) 829 BTU per degree-hour.
With a heating/cooling balance point of 65F and a 99% outside design temp, you have (65 - 6 =) 59 heating degree,
So the design heat load (at MOST) would be (59 x 829 =) 48,911 BTU/hr, call it 49K.
That's a realistic number for a house that size in CT with no basement insulation. It's a bit on the high side but not outrageously so. Since you're heating hot water with the boiler you can knock about 15% or more off that number- call it 42K, and if you insulate & air seal the basement knock another 15% or so off that, make it 36,000 BTU/hr, which (believe it or not) would be in the right ball park. After insulating and doing some air sealing I'd be surprised if your true heat load were over 40KBTU/hr @ +6F, but it probably won't be as low as 30K.
The smallest oil boilers out there have north of 70K of output, and if yours is 185K (input or output) it's operating efficiency is going to be well under the 85%, which is also contributing to the estimate hitting to the high side. But cast iron gas boilers come as small as ~30K, and there are a number of ~82% efficiency cheap 2-plate atmospheric drafted versions that run 50K-in/41K-out that would work. At your stated fuel use, resist the urge to install anything more than ~50-55KBTU/hr output, if cast-iron.
With a modulating & condensing boiler you'd be OK to be a bit over that, but not a lot- it needs to have a minimum-fire output of half your estimated 36-40K heat load to reap much efficiency from modulating, and if it's broken up into zones you may have short-cycling issues at low temp operation. The smallest boiler that actually meets the heat load at design condition is what you're looking for, since it will have the highest efficiency and fewest system design considerations to worry about. (The amount of baseboard on your smallest zone and the minimum fire output of the boiler will determine your lowest operating temp, and lower water temps are the only way to break in to the 90%+ efficiency range.)
On-demand tankless hot water heaters are as complicated as modulating condensing boilers, but have a range of issues to be aware of. From a cost/benefit point of view there's zero payback, but if you have a monster tub to fill or like to take 2 hour showers you might want one. With a boiler + indirect, size the tank for the biggest tub you'll ever need to fill, and if the boiler output is less than 100KBTU/hr (which it surely will be), use a zone controller that gives priority to the hot water, inhibiting other zones whenever the indirect is calling for heat.
The 1500' house with decent windows & insulation levels is going to come in at or under 30KBTU/hr, and even the tiniest cast iron gas boilers out there would heat it. With enough radiation you might do well with a "combi" heating system based on a tank-type condensing hot water heater, which would be less expensive than a modulating-condensing boiler, but run about as efficiently.
With most gas cast-iron boilers if there is so much baseboard out there that a right-sized boiler will never get hot enough that the returning water is under 130F there needs to be a short "system bypass" loop or similar plumbing configurations near the boiler to mix in boiler output with the returning water to keep the gas exhaust from condensing on the heat exchanger plates and rusting them out in short years. But cooler return water is exactly what you'd want with a condensing boiler, so "too much" baseboard would be push you toward the mod-con solution, or even a condensing tank HW heater (like the AO Smith Vertex, or Polaris etc.) with a plate-type heat exchanger isolating the heating system water from the potable.