1) No. Star Alliance rules said that (unless you're *G) you must depart the airport in question in Business or First Class. And I doubt that TAM leaving Star Alliance has made that policy more generous.

4) Small if this flight is very busy (and it frequently is). Before the flight opens for web check-in, LX will have pre-assigned seats to all pax which did not pick one themselves, and the single seats will likely be gone.