Heat rises, so the best place to start is at the top. I have an 1880 farm house; insulation is very tough. If you can zone get the house set up for zoned heating and AC, even better, esp. in leaky areas. For instance, I have a wing in my house I do not use except for the laundry. It has a separate (electric - EXPENSIVE!!!) heating/AC system, but if the temp outside drops below 20, I have to heat two of the four rooms that have the water pipes going through them. I have splits for heating and AC in there now, and a space heater in the bathroom where the laundry is. Tiny bathroom, so I close that door and use the ceramic space heater I have plugged into a thermostat in an outlet. Then I have to heat the main room, since the pipes run through and outside wall there to the bathroom. But this room is VERY leaky, ugh, and the upstairs bedroom and the bedroom off the bathroom I do not need to heat. So I put up plastic in those doorways, each with a Zipdoor zipper so that I can get through them if I have to, for instance to get to the laundry.

I would have an energy audit done to find out where the worst spots are and tackle those first.

If you have the old windows, they're likely really bad. wetting them with water (on the inside) and putting the flat side of bubble wrap on them REALLY works as great insulation.

Another important tip so many people either don't know about or forget about: if you have a wood-burning fireplace, which you likely do, make sure you close the flue in the morning when you get up and turn the heat on or up. And don't have fires when it's freezing cold out, unless of course you're entertaining and want it for the ambience. But chimneys are air tunnels and suck the furnace generate heat right up and out of your house! Of course, never close it before you go to bed on a night you've had a fire.

Air seal with caulk wherever you can. Insulate the attic/roof first, then the basement/crawl space. Walls tend to be the most expensive areas to insulate and the return in savings takes a very long time. Much better to put the money into the first two areas. Don't expect a great deal from the windows. Manufacturer's exaggerate the energy savings to a degree bordering on outright fraud.

I'd blow in a big pile of fiberglass insulation to the attic first thing. Easy to do, pretty inexpensive, big quick payoff.

With the crawl space, the biggest thing to do is seal off airflow into the house. Caulk, spray foam, etc. all the cracks. If the crawl space is vented, close the vents.

air sealing comes first. have a blower door test
done to find house leakage. make sure that you
follow the tester around & write down leakage
areas. keep a roll of tape handy to stick a piece
of tape @ leakage site.
if you get 'free' utility audit, you will have to
be there and slow it down long enough to get
an idea of where the leaks are.
to be told that you have an ELA (equivalent leakage area)
of a 3'x5' hole in the wall is not telling you where
leaks are. find out. step one.

heat loss/heat gain is through ceiling.
air seal from inside attic at attic floor & from
inside by caulking window/door moldings
to walls, ceiling moldings at top to ceilings,
bottoms to walls, caulk floor moldings to
walls & floors.

if equip/ductwork is in attic, make changes
there before adding insulation.
ducts can be tested for leakage also.
mastic materials should be the only material
used for a long lasting seal of ducts.

air seal at attic floor, then add insulation.

windows will get you between 7-14% savings.
not much for the thousands of replacement costs.
air sealing saves you the most
then insulation.
central hvac is biggest user, followed by
water heaters. invest in efficiency.

closed cell foam for under floors if on crawlspace.

not sure what payback for insulating walls would
be. here in my hot humid climate it isn't worth it,
but if it is for your area, hire it out.
the company can drill holes & pump in insulation.
vett insulation companies carefully.

is the house balloon framed?
if so recommendations change.

your house is eating up propane costs because
your house is like a leaky box.
stop the leaks, insulate & heat will stay inside
house instead of escaping through openings.

tell us more about hvac system type & location
of heating system & ductwork.
where are the return air(s)?

radiant barrier plywood will provide some savings
in summer, if house is in full sun. little to no savings
in winter. just fyi

best of luck.