the crawl space insulation doesn’t make much difference
attic insulation is a big deal, cellulose compacts over time and its highly likely that you may not have sufficient insulation, you can buy bulk fiberglass insulation at Lowe’s or HD and blow it in yourself, it’s a 2-person job and it’s easy if you don’t overload the machine, but, BUT, before you do that, it’s super important that you go in the attic with some canned foam and find every penetration that goes from your air-conditioned house into the attic, look for electric wire, plumbing pipes and light fixtures, uncover each one then seal them with the foam, this stops the air that is leaking between your house and the attic, stopping the leaks and adding insulation (if it is needed) can easily cut the bill 20-40%
windows would help, not so much for the double pane but much more for the insulation level of the frame and especially for the significant reduction in infiltration (air leaks)
infiltration is almost always the biggest problem, some of it is easy to fix on a 1 story house, first step is the attic, then windows, doors and outlets, then the crawl space, this work is a pain but it makes a big difference
there is a wide range of issues with ductwork, if the joints are sealed and there is just some missing insulation that’s an easy fix
bottom line is: seal the joints, insulate where the boots enter the house, make sure the return is properly sized and that it’s not pulling unconditioned air into the system, seal the duct work at the unit so it’s not pulling in unconditioned air and not pushing conditioned air anywhere except into the house
If the unit is oversized and the ductwork was sized for a smaller unit you have a problem that can be difficult to fix
PEOPLE - stop oversizing HVAC systems, terrible idea
shut the dang pool pump off, if you 're worried about it freezing put it on a timer to run a few minutes every hour or so, I don’t know the magic formula on this to prevent freezing, a 1 HP pump run 24/7 for a month costs