If one flies Southwest with a stop, do you get your seat assignments for both legs at the same time?
I can answer this part of your question. The answer is no you don't. When you arrive at your layover airport, you have to find one of their guest services desks in order to check in and get boarding passes for the next leg of your flight. At least that is how it was 2 years ago, and I doubt it has changed. We had a 1.5 hour layover and we received the last 2 A boarding passes and 1 B pass. I was glad we were not any later, but then again, it would not have mattered as the plane was maybe half full. We would have had no trouble getting seats together.
I have flown SW a few times, and we have never had trouble getting seats together for our family (3-4pp depending on trip). We just arrive early and line up in our row early and wait our turn to board

You should be fine as long as you get an A or B pass.
I personally use ATA over SW out of IND to MCO; because, they have way better flight times for us, and the price is usually comparable. Plus, you get seat assignments at booking

I also used to use Delta out of IND to MCO, but they changed their flights a couple of years ago, and the new times are not appealing to me. So for now I exclusively use ATA when going to Orlando
Good luck w/your flights
