Call a pro. AC systems are not DIY. The things you're looking for exist
(and are often mandatory) in the commercial/ non-residential market, but they are not IoT, and they aren't cheap. For instance, most commercial spaces have a MAX value on percentage of recycled air; a minimum amount of air fed into the return must be fresh air drawn from outside.
>should be able to cheaply add networked sensors, fans, filters, and vents
Sensors can be ok... But your homes's AC design, even if based on simple building code lookups, is based on some fairy complex engineering which rely on certain assumptions.
If those assumptions aren't met, the design usually must be approved by a licensed engineer. This is why you don't see more independently controlled vents on the market. No professional is going to install products that don't meet code, unless an engineer has stamped the plans. (Which includes operational logic.)
Ignoring regulations, you shouldn't just add controlled vents to a system (or manually close existing vents) without compensating for that elsewhere. You likely need a variable speed blower, controlled/compensated return air flow, and system logic to control it all.
Will the house blow up if you install them yourself? Probably not. But it could result in a system operating much less efficiently, increase the number of system cycles (reducing system lifetime), cause duct ruptures/leaks due to increased back pressure, and most likely, cause condensation in places other than the condenser, possibly causing mold to grow and/or rot.
Which leaves 2 options: installing a commercial system with the integrated vent control you're looking for, or adding sensors for input for when the system should run, without modification. Biggest simple change you can make for immediate impact? Change your filters every month, even if it means using 12 $3 fiberglass filters instead of 1 $36 hepa filter.
For instance, I run a list of room temps through a simple max function to ensure my AC and/or blower runs until the hottest room falls below the set temperature.
If this results in wildly unbalanced temps throughout the house, you have a bigger issue, and likely need your system resized/adjusted by a professional.
Related, and because most people don't realize it, your AC is an engine. You want it properly sized and to run constant, when needed. Think of your car: is it more efficient to make a trip by many intermittent 100mph sprints, or driving 55mph without stopping.
Multi stage compressors now act like car transmissions to dynamically "size" the system as needed, but run constantly with minimal stopping.