Been balancing my house.

Don't go to crazy closing off vents - there's an expectation of a certain degree of flow, and excess backpressure will reduce the effectiveness of your system.
Go with a low resistance filter, and change often - the filter is there to protect the equipment, not to clean your household air. Get a dedicated air filter if that's your aim.
Keep your Evaporator coil clean. Bust out the old nut driver and take a look - improved my airflow significantly.
Keep your condenser coils clean. Hose em off.

Current thought on the outside-ducted AC units is that they're probably counter-productive from an overall house perspective - the air going out has to be resupplied from somewhere, and that somewhere is probably from the outdoors through wherever air infiltrates your house. OTOH, if your cooling is generally sufficient and you need localized cooling, it's maybe not a bad bargain.