Now that the Dallas Texas weather is getting better for chores, there are some things that could make my a/c better. Its a 3 ton unit in a poorly insulated 1000SF house but it does well since I improved the return filter area. I may add some insulation but that is problematic/involved, may ask later. The indoor machinery sits on a hollow box serving as an intake plenum.

1. I've been told that if I like fresher air, I could bring in 50-100CFM from the outside and that this may also help reduce the amount (if any) of air coming in from the crawl space or attic. Will as much as 100CFM of fresh air from the outdoors impact the system in 100 degree weather? It is a small extra load including the humidity. There is a 4" unused dryer duct already making a run near there. I could replace it with new (its full of lint) and route it to the return air box if that is a good idea. an automatic damper would be easy.

2. The RH is about 50-60% with the a/c on in the summer. Is there any "feels cooler" advantage to it being lower? Is this something a dehumidifer would help, or is one of those be insignificant compared to the dehumidification done by the HVAC system?

3. There are two returns, a dual 12x24x1 in the dining room and the original 12x24x1 one in a bedroom (presently a catch-all room). Much air flows through the bedroom grille due to less resistance/ the way things were put together, - so the door stays open at least 4" for best airflow. If I put one of those above-door grilles in, the largest that would fit, will this let me close the door without much impediment to the return flow?

Thanks for your opinions!