Idiot rules watts (or BTU) per square foot rules of thumb heat load calculations are for idiots (but there are apparently still a lot of idiots in the HVAC contracting biz.) Ten watts per square foot is (10 x 3.412 BTU/watt-hour =) 34 BTU/hr per square foot, which is more than
twice the measured heat load of my (my sub-code antique) whole house, and the per square foot losses of the basement are lower.
The heat loads of even UNinsulated basements are usually MUCH lower than for above grade floors per square foot, and basements that are insulated to code have heat loads lower than that. Heat loss is a function of exterior surface area and temperature difference, not floor area. The peak temperature differences below grade are much lower than the temperature differences above grade.
An uninsulated 8" poured concrete wall has an R-value of about R1.35. If an uninsulated 2x4 wall is installed to the interior that more than doubles to about R4. When it's 0F outside, 70F inside that's a 70F difference, and every square foot of exposed above grade wall is losing 70F/R4= 17.5BTU/hr. The dirt below grade is at a warmer temp (= lower temperature difference) and has additional R-value (varies by soil type and moisture content).
Installing climate zone 4's R10 continuous insulation between the studwall and foundation (as you have) brings that up to ~R14, for 70F/R14= 5 BTU/hr per square foot of above grade wall, with even lower below grade losses.
Before installing the batts be sure to put a bead of polyurethane caulk between doubled up framing such as jack studs, window & door headers, etc, and seal the bottom plate to the foundation wall.
An R19 batt only performs at R
18 when compressed to 5.5" in a wall cavity, and does not really meet code, which is R20. The R21HD "cathedral ceiling batts work, as do R23 rock wool batts, or blown cellulose. A 16" o.c. 2x6/R20 wall typically comes in at about R17 "whole wall" after factoring in the thermal bridging and the R-values of the wallboard, sheathing, siding, interior & exterior air films, etc.
If the windows & doors have published U-factors, use those (U-factor x square feet x temperature difference = BTU/hr, 1 watt = 3.412 BTU/hr.) If they're clear glass double-panes (or single pane + storm), use U0.5, if low-E double panes, use U0.35.
For rough calculations only calculate the losses of the above-grade portions of the foundation walls + the first foot of area below grade as the placeholder for all below grade losses.
With heated conditioned space above, the losses through the ceiling are zero. The R30 was required when the basement walls were not insulated, but isn't doing anything useful after the walls are insulate. Just be sure the foundation sill and band joists are air sealed with polyurethane caulk before closing in the ceiling, and stuffing the band joist snug with that insulation.
Make a spreadsheet and run the numbers for the whole thing, using the
99% outside design temperature, (not the all-time record low.) Multiply by 1.4 (per ASHRAE) for an oversize factor to cover even colder temps, and the air infiltration, etc. For 575' of insulated walk-out basement you're probably looking at about 4000 BTU/hr, 5000 BTU/hr max of heat load at design temperature, (x 1.4=) 7000 BTU/hr to cover cold snaps, or (/3.412=) ~2000 watts, but it could easily be half that, which is why you run the numbers.
Installing 4000 watts when even 1500 would would cover the 99% design load or even the all time record load is even less comfortable, since the baseboards just cycle on/off at a low duty cycle even when it's cold out- the hot-flash followed by the chill. With right-sized heating equipment the duty cycle is 60% at design condition, higher when it's even colder, and there aren't any temperature overshoot or undershoots the baseboard will always be warm, and the room temperatures stay in a tighter band.
