let's talk strategy:

1. its a wednesday night flight (thursday 1:10am) people will buy S class ticket only for an upgrade. otherwise there are cheaper tickets.
2. looking at the seat map of the economy section, you see that all the preferred seats are free (22c, exit rows). this means that no GL/PL/TPL took those seats. this might imply that there are not many (if at all) gl/pl/tpl on this flight in economy right now.

3. there are 8 free seats in Biz + 2 more reserved for Crew

4. only one seat taken in First Class

taking all of this into consideration - if the flight was in the next few days, you would probably snatch an upgrade. but the flight is 3 weeks from now, and anything can happen.

what you might consider, and take a chance - you can get an S ticket and wait with the ticketing. (also S can be canceled without penalty).
if you see that biz gets crowded, you can re-book in a lower class.

good luck