Your troops can be armed with the usual collection of rifles and carbines, pistols including Lugers and the Mauser "Broomhandle." Machineguns would certainly include both Lewis and 1908s.
There was a lot of experimentation at the time and if anyone would have the prototypes, it would likely be the Kaiser or someone associate with him. Solthurn was experimenting with a machinegun that looks like a Bren gun but with a 20 round squared off magazine. The Czechs sere making a light Machinegun that eventually (1924) became populat with a side mounted magazine. It would certainly seem liekley that the Kaiser would have access to captured American BARs.
You can field submachineguns with side mount magazines, including a 32 round "snail" drum luger magazine. The Italians had a 1918 subgun that looks like the Baretta 1936/38 series.
Don't forget to give your guys fun little toys lie flamethrowers and rifle grenades. I would think those would get packed on the Zepplin ride. They might also pack along the Kaisers collection of hunting weapons including shotguns, large bore rifles and drillings and veirillings. The shotguns clould include pump and leveraction shotguns. Drillings are veirillings have 3 or 4 barrels respectivly. The Germans were big on those weapons as they gave the hunter several choices of game to shoot from the same platform. Usually they were 2 shotgun barrels and a third rifle barrel.
The other thought of how the Kaiser gets to China is by armored train. Just picture it, a large armored train, with zepplins in support, fighting across the revolution ravaged Russian countryside. Maybe recruiting a few cossacks and Russian ballerinas along the way.
Sounds like fun.