Hey, I play RuneScape for 5 years and I had a idea to start terraining RuneScape free world because I am not a member and I seen almost all places in free world, and because obviously your RuneScape project takes long to finish I can do the free world.
But about your story I got questions, how can a ORPG work if it has more maps, how can it work I mean? Can a ORPG work in seperate maps like the act 1 orc campaign?
If not I think there's a solution, you could make RuneScape in NewGen, the NewGen has 480x480 so maybe the whole free world can fit, if 480x480 it's not even enough for a free world then you could use the third-party world editor tool that has more than 480x480. But I assume if you make a 480x480 you will need many tiles, such for dungeon, so maybe you have to have seperate maps, or you need to create a map that has all tilesets in one map.
If you want to have a full area you must use NewGen, if the tilesets don't match to the map you may need to have seperate maps.