How deep is the cavity space between the metal-lath plaster and the brick? If it's more than an inch you can get a SUBSTANTIAL reduction in heat loss by having a contractor install
non-expanding injection foam. Do
not use expanding polyurethane foams in this application- there are too many expensive ways to screw it up, and the glue-nature of SPF makes removing/repairing any mishaps even more difficult. If it's only a half inch or so, it's probably not going to make much of a difference. With a narrow cavity you might be able to hit R6 for wall-R, but cheaper/better approach would be to add 2" of rigid iso on the interior, giving up ~3" of room dimension on the interior walls. This is a major undertaking, but if done all at once to avoid living in a construction zone, it would pay off in comfort & fuel savings in the long run.
With a 2-wythe brick wall and a ventilation cavity the wall's R value is going to be something like R2.5. If the windows are lower-efficiency double-pane (or have storm windows), they too are about R2.5, which makes the Manual-J type heat loss calc a lot simpler: Assuming a 67F interior temp and a +7F outdoor temp at design condition (6AM on the coldest days of the year), every square foot of exterior wall + window is losing about (67F-7F) x (1/R2.5)=24 BTU/hr.
So assuming a ~35' square exterior footprint with 9 feet between floors that's 35x4x9 = 1260 square feet of wall area. At 24 BTU/ft that give you:
24 x 1260=
30,240 BTU/hr.
Assuming you can easily get the roof/attic up to at least R20, the loss through the roof gives you
1100' x (1/20) x (67F-7F)=
3300 BTU/hr
Add them together and you're still under 35K, but if the ceiling, windows & doors are leaky you could be at 40-45K or higher, maybe even 50K if it's super-leaky, but still nowhere near the 77K output of the 4-plate Burnham ES2-4. With that boiler you'd be good down to about -50F, a temp not seen since the last ice age. The 3-plate ES2-3 would be a better choice, and run more efficiently after you've insulated & air sealed, brining the heat load down to ~30K or less (this IS do-able.)
But even the ES2-4 is such a large step down in input BTUs and up in efficiency that you will probably need a flue liner to narrow it down in order to avoid flue condensation rotting out your chimney from the inside over time. What it the cross sectional area of the flue?
If you intend to insulate the basement, insulate the basement walls, not the first-floor. If you insulate the floors it puts an R-value between the conditioned space and the boiler, so the standby and distribution losses of the boiler are all lost, rather than accruing to conditioned space. If you insulate the walls the basement stays warmer & drier, and the standby losses aren't fully lost.
To figure out the best way to insulate it, what type of foundation?
In the attic, blowing in cellulose will be more effective than fiberglass, due to the high convection losses of blow fiberglass in a warm side down configuration. The buoyancy of the air warmed by the ceiling moves relatively freely through even a foot of low density fiberglass into the cold attic air, making low-density fiberglass perform way below spec when it's 25F or less in the attic. By contrast, cellulose is more air retardent, and has a fairly stable R value across temperature. Use only "sulfate free" or "borate only" goods though- cheap sulfate fire retardents are corrosive when wet (and stinks when wet too), whereas borates are benign to metals & humans, but toxic to the gut-flora of wood boring ants/bees/wasps/termites, rendering them unable to digest wood.
Simply blowing insulation blindly into the attic isn't a good idea, since you can't tell where the insulation is going or how much there is. If there isn't an access hatch, make one, even if it's in a closet or hall ceiling. Insulation that blocks soffit ventilation and jams up against the roof deck can cause localized rot areas on the roof deck & rafters.
More. If the wall cavities vent into the attic and you block them off with fiber insulation blown into the attic you may end up with moisture issues bleeding through causing the paint, then the plaster to fail on in your cavity-wall. (With non expanding injection foam this is less of an issue, but it's important to use a high-quality silane/siloxane masonry sealer on the exterior if you fill the cavity. Non expanding injection foam is vapor permeable, but waterproof, and the high water vapor drives of summer sun on rain or dew wetted brick can also cause paint failure in that configuration, even through the foam.)
Reflective paints on interior rooms have almost no effect on heating bills, but slipping in aluminized radiant barriers between the radiators and walls will be worthwhile (or even cut up sections foil-faced 1" iso), at least until you've figured out how to better insulate the walls fully.