You don't really need a map because there's only limited number of roads and streets - and if you'll walk the trail between Yung Shue Wan ans Sok Kwu Wan there will be signs.
You will come accross this large map at the piers when you come to Lamma. It's enough information for your short visit there, and... as you walk further you'll see along the way some most interesting sights from the trail... or in some cases additional signs will point you to other things to see. No worries, you wont get lost if you use main trail - it is indeed small island.
Many people take the ferry to this island in order to sample one of the seafood restaurants. I ate at Sok Kwu Wan before taking the ferry back to Hong Kong. There was an entire row of restaurants available. The seafood is typically swimming alive in a row of tanks on display for you to see. You can choose which sea creature (s) you would like to eat and they will cook it for you.
Fondest memory: Eating at an outdoor restaurant overlooking the harbor.
Favorite thing: When you take the ferry to this island, don't forget to bring your bathing suit. There are some nice beaches on the island. Hung Shing Ye beach can be found not far from Yung Shue Wan. It is an easy walk to this sandy beach. There are some facilities such as changing rooms and drinks/snacks available here. Most important, a shark net protects the swimming area.
This one activity that I highly recommend while visiting the island. I also suggest taking the ferry into either Sok Kwu Wan or Yung Shue Wan and then walking from one to the other. If you would like to eat first, I recommend Sok Kwu Wan as the first stop. If you want to swim first, then go to Yung Shue Wan. Walking between the two towns takes 1-2 hours depending on your pace. There are excellent views all along the way. Bring plenty of water and sun protection since this is a tropical setting. There will be some uphill and downhill travel at times. By all means, bring a camera. The towns and the shoreline are very scenic, except for the power plant at the north section of the island. Fortunately, you will not see it for much of the hike.
Fondest memory: Seeing the rugged coast and picturesque towns while hiking this trail.