Easiest way to fill up gearbox : 20litre drum with a drum pump and a small nozzle that will fit in the filler plug(looks like a little square shaped plug) - I think an open end 9'16 or 14mm ring spanner will undo it. This is also the level plug for your gearbox oil. I'm not sure what country you're in but I have used BP Energear easyshift oil for the gear box. Fill it up till it runs out the filler plug as this is also your level.
The drain plug is underneath (Obviously...)

As for the clutch an easy job.
Rip off the starter motor, gearbox etc.
When you are looking at the clutch undo the ring of bolts around the outside.
She'll all come apart nice.
If you have got an old input shaft use that to line up the new clutch assembly in the spigot.
Make sure you gease the spigot bearing.
Always clean the flywheel down very good with emery paper and make sure there is no oil or anything on it.
If in doubt and it looks like there are any hot spots on the flywheel - Get it machined.
If you wanna "spin up the wheels" u might as well get them to lighten and balance the flywheel while its out.........................................other than that spend some money on the donk........................