I have 2 Qs: 1) Is it feasible for 6 adults of 6 luggages (5 big ans 1 handcarry size) 2) Do we have to purchase at Shilla Duty Free on the first day? If not, how can I provide the proof later? 3) What if at the end we can\'t purchase up to US$300. What\'s the back charge then? Thanks for your advice.