Wow Cameron, thats a great thing on your application to study for being a vet. That another farmer/smallholder is happy to trust you with his flock at the most difficult time of year for it.
You'll be fine, how many ewes does he have and how any are still to lamb? Keep an eye on them, if any show signs of lambing, ie straining or discharge and aren't getting anywhere within about 1/2 an hour, then you will probably have to help them.
If any lamb outside, make sure you keep an eye on them for crows too- horrible horrible creatures.
Beth