LAX-STL Flight Question under the new SWA regime

I"m looking into booking a flight LAX-STL in mid-May. Southwest is the major airline with non-stops for the route, now that TWA is gone. My wife has had a knee replacement and can't do all the airport terminal walking (although she can walk down the airplane aisle), so we legitimately need wheelchair assist. I've read through the recent posts, and don't see an answer here:

(1) Is wheelchair assist still the same as usual, with pre-board for the passenger and the person with them?

(2) Assuming I want to pick our seats (and back of the aircraft is fine), I'm guessing I need the Choice fare. Is this now working reliably under the new system, or is SWA still screwing up and ignoring your in-advance seat assignment?

(3) Is SWA still too unstable to trust, and I should look instead to a more reliable carrier and deal with a change of planes?