and to want to work out different alternatives based on numbers that work for YOU. I don’t have a lot of experience with A/C since we have the entire Pacific Ocean serving that purpose out here. But having spend time in the mid-Atlantic states a few decades ago, I remember enough of what it was like.
Two suggestions –
1) we try to think in terms of the “goldilocks solution” here – not too much, not too little, but just right. That Lennox sounds like a top-of-the-line model (and the A/C company would probably make commission on that sale, so they are motivated to get you to spend as much as possible). You might want and need A/C, but that would be the single most expensive option for you to take.
2) Home Depot and other big-box stores sell a wider range of products, from El Cheapo to High Quality, but they have a very big markup on most of their products. In other words, if you decided on X model, they would have the largest markup on that X model above and beyond the MSRP.
For all of our major appliances over the last 10 years, we’ve first chosen the general capacity we wanted, THEN chosen a model or a few models that provided that capacity, THEN shopped aggressively for that model. We have consistently found that Home Depot and the like are the most expensive sources for any given big appliance. For our water heater for example, I think we paid $500 for it from an online direct-from-manufacturer dealer, and the Home Depot list price was $899. There was that big a difference.
I can’t advise you on what model or capacity you’d need, but you should already have that from the estimates you’ve gotten. Work from those estimates to figure out how big a system you need, then start shopping online for those units or units like them. You might be amazed to see how much less expensive it would be to go that route.