Generally you don't need much of a chuck on whitley, 40-50 yds is about right. As to where to fish - that's the 64,000 dollar question. It's generally best fished when there's a good northerly sea crunching in and the tide's not too big, as a lot of the marks will empty out over low water.
If you're not too familiar with the area I'd suggest starting around the Panama area, or in Big Bay (to the left of the rendezvous cafe) about 2 1/2 hours before low water. As the tide drops back you can move onto the rocks in front of the cafe (Wilkies) or to the left of Big Bay you've got North Skeer. To the south end of the beach you've got Old Salts Hole & the Half Moons, but they're both best fished early as they'll begin to empty out. It's all pretty mixed ground, some marks a bit heavier than others, but order of the day is usually a simple 2 hook flapper, 1 up 1 down, and experiment with baits to see what the fish are taking. I'd definitely want crab, lugworm & maybe a bit of razor & mussel.
If after a few chucks you've had nothing, then move. That's the key to this beach, the fish can be very localised, and you've got to be prepared to hunt them down.
Gary