Nobody else has suggested anything, so I will throw out some uninformed opinions.
Every Japanese machine I have ever seen (I own ten) uses some variant of JD303 or International Hy-Tran in the gearbox, which usually serves as the hydraulic reservoir. A couple Mitsubishi machines have separate reservoirs for the differential, and the transmission serves as the hydraulic system reservoir.
Most any hydraulic fluid will work in the simple, straight gear drive machines. Any tractor dealer should have a product labeled "Universal Tractor Fluid" or some such.
The front axle requires lubricant. I run gear oil in mine, but many machines come from the factory filled with the same hydraulic fluid as in their transmissions. There is possibly a drain on each end of the axle.
The trick to all these lubricants is that they are all about the same viscosity when warmed to their recommended operating temperature. I think the additive package in a dedicated gear oil is advantageous, but it also is much more important that the machine have any lubricant as opposed to none or only a tiny amount of the perfect substance.
I don't have a clue on the cable from the dashboard. Many of these machines had extremely complex controls for their factory-mated rototillers, able to control the depth, pitch, tilt, and other factors to optimize performance in the rice paddies.
Can you take some photographs?
The air filter sounds like the standard cartridge type. Take it to a good parts store or tractor dealer. They will be able to match it.
Good luck!