I am looking for a cheap fare ATL-???-ICN & ICN-???-ATL in June.

I took SQ ICN-SFO three times (1996, 2003 & 2005). Last time in 2005, I took UA DCA-ORD-SFO and SQ from SFO. Advanced seat assignemnt was not available for SQ. I was told by UA agents at DCA that my bags were going to ICN but I had to get the boarding pass at SFO SQ couter.

Is it the same story today?
1) no seat assignment on SQ?
2) boarding pass at SFO only?
3) If I take DL or FL on ATL-SFO, do I have to recheck my bags? (I think FL may not have agreement with SQ)

Usually 2stop UA (ATL-ICN roundtrip) is $1200 in June. Somehow it is over $1600 this year. I am looking for SQ($1200 with mile accumulation) + ATL-SFO on DL or FL ($300+). DL ATL-DTW-ICN is $1470, but I would like to avoid UA E- or DL E on trans-pacific segment.

Thank you.