What are the requirements for an I fare? How about for a B fare?

I'm looking at BKK-HKG-vv. in late December. Should be a low level of business travellers but a high number of liesure travellers-- unclear to me how many would be paying for Business Class. Right now, everything is pricing out as a full J fare, about US$700 roundtrip. Is it just too early to see any discounted fare classes? Anyone have suggestions? My status is on Delta; no status on any oneworld carrier.

We'll be two pax travelling together both ways. Does CX ever do Two-to-Go promotions for Business Class? If so, when would those appear online?

As an alternative to buying confirmed J tix in advance, would you recommend just buying mileage-earning Y tix and buying the upgrade for 5000baht at the airport?

Many thanks in advance.