Did they have to pay any war reparations, and what was their opinion on the "Big Four" (USA, GB, France, Italy) and the war reparations they should pay?
edit: Also, does Japan have anything to say about Self-Determination in WW1?
Er, Japan was on the winning side of WW1. So I don't think they had any problems about it.
Japan was generally quiet during the Versailles conference unless it was a matter that directly impacted their interest. E.g. Shandong peninsula.
The only interesting thing Japan proposed at Versailles was the Racial Equality clause. But it got watered down and eventually dismissed (the clause required a unanimity for it to be adopted and it failed to get that).
They were a pretty big fan of them, actually. Germany had a sphere of influence in China, and Japan's only real action during the war involved moving to ensure that German protectorates and possessions were taken, and the Germans were prevented from using sea lanes in the Pacific to resupply. They demanded (and received) Germany's holdings in Shangdong as part of their war reparations, and later had Germany's holdings in the South Pacific put under their control by the League of Nations as part of the South Pacific Mandate. This was what enabled them to fortify the islands, in turn requiring the use of the island-hopping campaign by the US during WWII.
There's a look at how all this played out in Dickinson's War and National Reinvention, including an interesting discussion of how pro-British politicians were able to overcome the objections of pro-German military leaders (the Japanese army was reconstituted along Prussian lines during the early Meiji era, and the officers retained their approval of Germany) to side with Britain during the war.