I found out how to easily implement zoom functionality:
final MapWidget map = new MapWidget(startLatLng, 12);
map.setSize("100%", "100%");
MapUIOptions options = map.getDefaultUI();
options.setScrollwheel(true);
map.setUI(options);
For more info check out maps demo. You can checkout project code and test it in eclipse!
I'm still searching for solution to other problems.