Not a "real home improvement" guy, but my dad added radiant barriers to his attic some year back. I want to say he said he saw a ~15% reduction in AC usage back then which reduced the ~$300 bill (in peak summer) by about $50.

Radiant barriers always seemed like a low hanging fruit solution to help with summer cooling.

I'm a fan of insulating first because I find it more pleasant to have the house stay at the same temp longer rather than cycling between too hot and then too cold when the AC is running every couple of minutes.

We did a combination of R-38 batt insulation in the attic and blow in (i.e. drill & fill) for the exterior walls and it's helped tremendously. Also, we added radiant heat barriers in the garage where there's no HVAC. We had pros install all of this since it is fairly labor intensive to crawl around in the attic. They knocked it out in 2 days.

Another thing we did was get solar panels. Depending on your state's current net metering policy, this could more than offset your entire usage. For us it made sense since we were also getting an EV in addition to having ever-increasingly hot summers.

If I had to replace the AC unit, I might look into a heat pump/mini-split like you mentioned since you don't have to cool/heat the entire house if you don't need to, but ours is still fairly new.

You want to insulate first, otherwise anything else you do is just going to be pushing heat through your exterior walls. You should be able to get spray in insulation in those walls without needing to full tear down the drywall. Typically you’ll get a 1-2” hole on the top and bottom of each stud bay for foam to be sprayed in, then you patch that. It can be pricy up front but should pay off super quick if you have none right now (I’m still getting over 3,000 kWh… that just seems like an insane amount of electricity to use).

A mini split likely won’t help, you’ll just lose the cooling without insulation the same as without the mini split. You may want to look into balancing your ducting once you get the house insulated if you still have rooms that are too hot or cold. The bricks should help to stabilize temps and reduce swings over time but the effect is likely small and should be able to be ignored once you insulate.

Is there insulation on the exterior walls? If not then that seems like the biggest/best single thing to do. I would bet there's some way they can shoot in some without destroying all the walls but idk.

I don't see how a mini split, which is generally less efficient than a typical outdoor unit, helps at all.

Spray foam insulation is another thing to investigate for the attic.

Also, and this is outside the box, what about planting some trees to throw shade?

General order of operations

-When is the last time your AC was serviced? Are the filters or condenser coil blocked with dirt and dust and killing it's performance? Is the condenser installed under a deck or somewhere stupid with no airflow?

-Fix air leaks. These are the biggest loss of energy. You can diy or have someone preform a home energy audit where they hookup a fan to see how much air loss there is. Then seal gaps, replace worn weatherstripping, etc and retest. There are incentive programs here in many states to help pay for these audits

-Is you attic properly vented? Look for soffit vents and ridge vents. You may only have gable vents in an older home which is not going to cut it. Your attic becomes an oven if it's improperly vented. There is a certain ratio of ventilation to square footage of attic that needs to be met, 150:1 if I recall.

-Insulate attic: You didn't specify your region but 8 inches of old fiberglass isn't going to cut it in the majority of regions. That could be as little as R20. Adding additional insulation to the attic is cost effective and there are incentives programs to do so. Check what the recommended r value is for your zone. R49 will cover most of the US if I recall.

-insulate walls: You don't need to tear down the drywall to insulate. They drill holes into each joist bay and blow loose fill insulation in. Then patch all the holes. Same as attic but slightly more work.

-windows: are your windows/storm windows using double pane glass? If they are, how old are they? have their seal been broken? Also look into curtain treatments for windows that get heavy sun.

The very last thing you should do is be looking at replacing HVAC gear. If you do it out of order then you'll buy oversized equipment that will short cycle when you add insulation.

Also more generally, trees. Plant them. Let them get big and grow around your house for shade. Not exactly an overnight fix but mature trees can reduce massive thermal loads. Especially if they shade your AC from direct sunlight.

And one last note, please don't add vinyl ontop of your brick veneer. That's a great way to devalue your home. Yes technically you can put vinyl up with a layer of foam insulation board underneath but that's really a last resort.