Gearbox / Clutch Fluid
I have used a variety of ATFs (automatic transmission fluids). My current choice is Valvoline Dexron VI, mostly because it is a full synthetic that is readily available and inexpensive. You will have your own favorite, which will probably be just fine.
Clutch Hydraulic Fluid
I have been using Magura Blood because it is readily available in the US. A mineral oil must be used, preferably one with a very low viscosity. I have used a 3-weight suspension fluid in a pinch. It seemed to work okay, but I eventually purged it, as I think some of the clutch's feel comes from the viscosity of the fluid. Magura Blood is like water in that regard.
Do not substitute DOT3 or DOT4 brake fluid. The seals in a mineral oil system are incompatible with the seals used for DOT brake fluid. Although DOT brake fluid was used for some hydraulic trials clutches, the slave cylinder was mounted external to the engine. When the slave cylinder is mounted inside the engine, there is the possibility of gearbox oil coming into contact with the slave's seals. Hence the requirement for a mineral-based hydraulic fluid.