Sometimes oil specifications change during a vehicle's production run. Your starting point of reference should be the handbook that was supplied with the car when it was new.
If you don't have yours, you could use the information from mine (at your own risk); it's for a 2010 1.2 500. The specification is a fully synthetic lubricant to specification API GL4 PLUS or FIAT 9.55550, grade SAE 75W-85
No, just use gearbox oil which conforms to the manufacturer's specifications. Given the high mileage, do check the clutch hydraulics are up to scratch (unlikely if they're original); the new clutch might not last long if the actuating mechanism isn't working properly.
Make sure you have correctly identified the drain plug; there's another thread running at the moment when someone removed one of the detent plunger plugs by mistake. Also remove the filler/level plug first, or you'll get a partial vacuum in the gearbox which will both stop the oil draining freely and possibly pull contamination in past the seals.