Engine cambelt and clutch questions

[Whos Adam?]

When Idling the revs shift about a little bit, which seems fine however sometimes they just drop to around 500 rpm and the whole car shudders. It is only brief but makes me think something is wrong.

Wondering if anyone has encountered this before and what it could be? i thought maybe ECU.

Also i don't know if my car has had its cambelt replaced or what kind of mileage it needs doing at, Its a polo mk6

and finally My car is starting to feel a bit rough on gear changes and setting off in 1st, I'm hoping i will get longer out of the clutch but just in case, How much would a replacement cost, Fitted?

Cheers guys!