Since you'll qualify for pre-boarding (and shouldn't have any problems all preboarding since your DS is 8), you do not need to purchase EBCI. Normally they limit to one person pre-boarding with the disabled person, but your son is young enough that they'll include him. (Quite honestly, the majority of times I've flown with both my parents, they've let them both pre-board anyway.)
I've flown quite a few airlines (both domestic and international) with my wheelchair and SWA is definitely my favorite for domestic flights. It may be worth finding out ahead of time whether your flight is originating at your airport or not. Flights originating somewhere else often don't usually require you to turn up quite as early (pre-boarding usually is about 20-30 min, if that much, before scheduled takeoff for those flights). On flights that originate where I was boarding, I've been pre-boarded as much as 45 minutes before scheduled takeoff (one of the earliest of any airline I've ever flown with). Because I'm usually the only person pre-boarding using a personal wheelchair, I also tend to be preboarded first. The only times I haven't been were other flights with people who had a personal wheelchair or the time when one of the other women pre-boarding pushed around enough to make it impossible for them to take someone else down first (she was actually blocking the ramp to the plane). Both situations are incredibly rare for me. The other thing is if you're not in the first leg of that SWA flight, there may be people already sitting in the seats close to the front that are easiest for people preboarding. I've seen this handled a couple ways. Most often, the flight crew asked anyone who isn't disabled/accompanying a disabled person to move farther back in the plane. Occasionally, they've just made sure there were enough closer spaces to fit those people preboarding, and at least one member of their party, in the first 5 or 6 rows, rather than just the first 2 or 3.
I will say that I usually much prefer the second row to the first/bulkhead. For me it's just due to ease of accessing my things (including meds) during flight and, especially, during takeoff and landing. I can, however, walk a couple steps. If I couldn't walk at all, I'd be more open to the bulkhead. Every SWA flight I've been on, they could get my wheelchair up to the bulkhead seats (which is why I can actually get to the second row). I don't know that if you could easily do a straight lateral transfer that way, but stand & pivot or lateral on an angle should be possible. Do not be afraid, however, to ask for an aisle chair if she needs one.
