Peak travel for chinese new year will start from this thu/friday 19 Jan and will probably lighten up after 29 Jan. People are not just traveling home, they are taking the long holiday to travel, hence you have most of the asia routes fully booked in all kinds of direction.

I would recommend a set of nice clothes if you are taking asian airlines but they might give you the slack if they see you are back packing. But if you are fighting for seats, then you would hope the dress code makes a diff (though I've experienced otherwise, a guy dressed like a bum got ahead of me maybe because he has other priorities)

I'm not sure where you heard they don't oversell, everyone is overselling these days. Worse case scenario, take the budget airlines out if you are stuck but I hope they have better safety standards now.