........."Keep in mind that while you may be in the A group in Nashville, there may already be a half full plane when you board because SWA uses BNA as a hub for the south!..................."
I learned this too when I came out from CA to Orlando but we had to switch planes in New Orleans. My daughter and I got "A" boarding passes for the New Orleans leg (which I thought hooray!) so I didn't bother waiting in the A line but found out when we got on board that it was already full of passengers!
My daughter and I had to sit separately. (Not really a problem this time, just across the aisle).
The best thing to do with your "A" , "B", or "C" boarding pass is to stand immediately at the front of that letter's line, no matter how long before your plane takes off, espcially if you are boarding a through flight. That way even if there are others already on board, you'll be in front of the 30 other people who also have the same letter boarding passes as you and therefore better chances to sit with your family.
....."Of course we will have lots of luggage to check so I didn't know if printing boarding passes out after midnite would make a difference or not............"
It won't matter how much luggage you have as it's not related to the boarding passes. You'll still have to check your bags in BUT you'd have your boarding passes already taken care of if you printed them out already. I want A boarding passes so I'll try for them ahead of time & if I get them that would be one big worry taken off of my shoulders! (Not that I wouldn't arrive at the airport at the recommended time) just that knowing what passes we have is a relief. I've also been to the airport in plenty of time only to see all the A's taken before we got to the counter
Good luck! Tammy