Here are the results of some testing:
1. sn-special-attack-type3 doesn't do anything. With this set to both 0 and 1, wonders are always targetted first when there is no current fighting. If a castle is shooting at an allied unit, etc., then the wonder is often ignored. Again, there is no change in behavior between a setting of 0 and 1.
2. The sn-maximum-town-size attack method works on all map types, including across water. (The "town" is not restricted to a single island.) However, soldiers will not use transport ships unless you give them the attack-now command. If sn-maximum-town-size is set large enough to include enemy buildings on another island and soldiers have no way of walking there, then the soldiers will just stand idle - they won't choose another target that they can reach.
3. Ships do not participate in sn-maximum-town-size attacks, even against docks. Ships will target only ships and docks when given the attack-now command. Other types of units and buildings will be targetted only if they are in the line of sight of the ship after another target is destroyed - the only things that ships will move to attack are ships and docks. However, ships will respond to attacks against allied units by any type of enemy unit or building. The important point is that ships will not move across the map with the intent of attacking a wonder; they will only attack a wonder if they happen to be nearby after attacking something else.